Answer: Intracholecystic papillary neoplasm

Final diagnosis:  

Intracholecystic papillary neoplasm

Educational Objectives and Discussion:

Educational Objectives

1. To understand the definition of intracholecystic papillary neoplasm
   (ICPN) of the gallbladder by 2019 WHO Digestive System Tumours.
2. To recognize the gallbladder lesions associated with metachromatic
   leukodystrophy (MLD), an unusual neurologic disease in pediatric patients.
3. To discuss the differential diagnosis of ICPN.

Discussion

Intracholecystic papillary neoplasm (ICPN) is a precancerous lesion of the gallbladder. Per the 2019 WHO Digestive System Tumours [1], ICPN encompasses/replaces the previous terminologies, including biliary
adenoma, tubulopapillary adenoma, intracystic papillary neoplasm, and papillomatosis. Grossly, these tumors form distinct polypoid/exophytic intraluminal masses that are grossly visible. Microscopically, these tumors show papillary and/or tubular configuration with varying degrees of epithelial dysplasia. There are four morphologic patterns recognized: biliary, intestinal, gastric, oncocytic, or combination of these. These morphologic patterns contrast with classifications of intraductal papillary mucinous neoplasms (IPMN) of the pancreas in which oncocytic lesions (intraductal oncocytic papillary neoplasms (IOPN)) have been separated from IPMN due to distinct molecular findings. Mucosa surrounding ICPN may demonstrate dysplasia as well. About 50% of ICPNs are associated with invasive adenocarcinoma, but they have a better clinical outcome than conventional gallbladder adenocarcinomas [1, 2].

Our case exhibited low-grade ICPN with combined biliary, gastric, and intestinal differentiation. Adjacent mucosa also showed diffuse low-grade dysplasia. No high-grade dysplasia or invasive carcinoma was identified in extensively submitted sections. The aforementioned unusual findings in the gallbladder from a 2-year-old baby triggered further work-up since there is a well-known association between ICPN (previously called gallbladder papillomatosis) and metachromatic leukodystrophy (MLD) [3-5]. Genetic analysis was performed and the results revealed homozygous deletion of pathogenic variant c.1283C>T (p.Pro428Leu) in ARSA gene, which is associated with MLD. Brain MRI findings were non-specific and she has no history of developmental delay, neurologic symptoms, or regression.

MLD is a lysosomal storage disease caused by a deficiency of arylsulfatase A (ASA) with autosomal recessive inheritance in most cases. The ASA deficiency leads to the accumulation of sulfatides in the central and peripheral nervous system, which results in the destruction of the myelin sheath and eventually leads to neurologic symptoms such as seizures, loss of motor functions, and peripheral neuropathy [6]. Sufatide accumulation is also detected in other organs, e.g., the gallbladder, kidney, lymph nodes, liver, and bone marrow. The gallbladder epithelial cells and macrophages contain cytoplasmic inclusions on electron microscopic examination, consistent with sulfatide accumulation [3, 7]. Almost all case reports described the presence of collections of the lamina propria macrophages in the gallbladder [3, 4, 7, 8], as seen in our case (Figure 4). This accumulation of macrophages could show histologic overlap with cholesterolosis, a more common finding in the gallbladder. In MLD, Giemsa and toluidine blue stains will show metachromasia of the cytoplasm of macrophages, consistent with the accumulation of sulfatide deposits. In contrast, the accumulation of cholesterol esters and triglycerides can be highlighted on frozen tissue with Oil red O or Sudan black stains.

According to the age of disease onset, there are three clinical subtypes of MLD, including late infantile-onset, juvenile-onset, and adult-onset. Our patient showed no neurologic symptoms but was homozygous for mutation of the ARSA gene, which encodes ASA. Numerous mutations in the ARSA gene have been identified, and c.1283C_T mutation in our case is usually seen in juvenile or adult-onset phenotype [6]. That may explain the neurologic symptom-free status of our patient. A possible treatment for MLD so far is hematopoietic stem cell transplantation for selected cases [4]. MLD-associated gallbladder abnormalities occasionally appear before the onset of neurologic symptoms or an MLD diagnosis [3]. One case series with 34 patients reported that 76% of MLD patients showed gallbladder involvement [4]. The gallbladder abnormalities consist of benign and malignant conditions, e.g., cholecystitis, cholelithiasis, mucosal hyperplasia, polypoid lesions (now most lesions are under the category of ICPN), and adenocarcinoma [3-5]. In conclusion, gallbladder abnormalities, in particular polypoid lesions, are rare during childhood. This condition can be seen in cases with MLD, Peutz-Jeghers’ syndrome, and pancreaticobiliary malunion [8]. Pathologists should pay close attention to unusual gallbladder abnormalities in pediatric and adolescent patients to consider the above-mentioned possibilities and associated risk of malignancy.

Differential diagnosis:

Pyloric gland adenoma is composed of lobules of small, tightly packed, bland-looking glands that are morphologically similar to pyloric or Brunner glands. The uninvolved gallbladder mucosa is mostly devoid of dysplasia or pyloric gland metaplasia. Of note, pyloric gland nodules <0.5 cm arising in a background of pyloric gland metaplasia should not be designated as pyloric gland adenoma [9].
Reactive epithelial hyperplasia, commonly due to secondary causes (e.g., cholelithiasis, chronic cholecystitis, inflammatory bowel disease, primary sclerosing cholangitis), shows focal or diffuse papillary-shaped and elongated mucosal folds lined by bland epithelial cells with or without metaplastic changes. The presence of significant inflammation and no discrete, grossly visible mass-forming lesion, may help distinguish reactive hyperplasia from ICPN [1,10].
Invasive adenocarcinoma is present in about 50% of the ICPN cases at the time of diagnosis [2]. Gallbladder adenocarcinoma arising in ICPN is more commonly associated with papillary growth patterns, biliary epithelial lineage, and high-grade dysplasia. The invasive component is often a tubular adenocarcinoma, although other types, such as mucinous, adenosquamous, or neuroendocrine carcinoma, have also been reported. Extensive sampling is warranted because approximately 60% of ICPN with carcinoma showed ≤ 5mm of invasive focus, and the carcinoma may also occur away from the main ICPN lesion. Some patients with non-invasive ICPN can also die of new primary carcinoma in the biliary tract, typically long after the diagnosis of ICPN, possibly due to the field cancerization phenomenon. This observation supports long-term surveillance of these patients with ICPN even after resection [1, 2].

References:

1. Basturk O, Aishima S, Esoposito I. World Health Organization Classification of Tumours. Intracholecystic papillary neoplasm. In: Digestive System Tumours. 2019, IARC, Lyon.
2. Adsay V, Jang KT, Roa JC, Dursun N, Ohike N, Bagci P, Basturk O, Bandyopadhyay S, Cheng JD, Sarmiento JM, Escalona OT, Goodman M, Kong SY, Terry P. Intracholecystic papillary-tubular neoplasms (ICPN) of
   the gallbladder (neoplastic polyps, adenomas, and papillary neoplasms that are ≥1.0 cm): clinicopathologic and immunohistochemical analysis of 123 cases. Am J Surg Pathol. 2012 Sep;36(9):1279-301.
3. McFadden K, Ranganathan S. Pathology of the gallbladder in a child with metachromatic leukodystrophy. Pediatr Dev Pathol. 2015 May-Jun;18(3):228-30.
4. van Rappard DF, Bugiani M, Boelens JJ, van der Steeg AF, Daams F, de Meij TG, van Doorn MM, van Hasselt PM, Gouma DJ, Verbeke JI, Hollak CE, van Hecke W, Salomons GS, van der Knaap MS, Wolf NI. Gallbladder
   and the risk of polyps and carcinoma in metachromatic leukodystrophy. Neurology. 2016 Jul 5;87(1):103-11.
5. Kim J, Sun Z, Ezekian B, Schooler GR, Prasad VK, Kurtzberg J, Rice HE, Tracy ET. Gallbladder abnormalities in children with metachromatic leukodystrophy. J Surg Res. 2017 Feb;208:187-191.
6. Cesani M, Lorioli L, Grossi S, Amico G, Fumagalli F, Spiga I, Filocamo M, Biffi A. Mutation Update of ARSA and PSAP Genes Causing Metachromatic Leukodystrophy. Hum Mutat. 2016 Jan;37(1):16-27.
7. Rodriguez-Waitkus PM, Byrd R, Hicks J. Metachromatic leukodystrophy and its effects on the gallbladder: a case report. Ultrastruct Pathol. 2011 Dec;35(6):271-6.
8. Garavelli L, Rosato S, Mele A, Wischmeijer A, Rivieri F, Gelmini C, Sandonà F, Sassatelli R, Carlinfante G, Giovanardi F, Gemmi M, Della Giustina E, Amarri S, Banchini G, Bedogni G. Massive hemobilia and
   papillomatosis of the gallbladder in metachromatic leukodystrophy: a life-threatening condition. Neuropediatrics. 2009 Dec;40(6):284-6.
9.  Basturk O, Aishima S, Esoposito I. World Health Organization Classification of Tumours. Pyloric gland adenoma of the gallbladder. In: Digestive System Tumours. 2019, IARC, Lyon.
10. Umudum H, Gunbatili E, Sanal M, Ceyhan K. Primary diffuse papillary hyperplasia of the gallbladder. Pathology. 2006 Dec;38(6):591-2.

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Case contributed by:

Goo Lee, MD, PhD. University of Alabama at Birmingham

Rong Li, MD, PhD. Children’s of Alabama Benjamin Russell Hospital For Children

Conflict of Interest: NO

Answer: Mucinous cystic neoplasm

Final diagnosis:  

Mucinous cystic neoplasm

Educational Objectives and Discussion:

Educational Objectives

1. Discuss spindle cell lesions of the pancreas.
2. Review the clinicopathological characteristics of mucinous cystic neoplasms of the pancreas.
3. Identify an unusual presentation of mucinous cystic neoplasms with stromal overgrowth.

Discussion

Immunohistochemistry stains were performed, and the spindle cells were positive for estrogen and progesterone receptors (Figures 6-7) and focally positive for inhibin. The spindle cells were negative for CD117, DOG1, S100, pan-cytokeratin, and beta-catenin. The proliferation index assessed with Ki-67 was approximately 1%. Based on the lesion’s morphology and immunoprofile, the case was diagnosed as mucinous/non-mucinous cystic neoplasm with ovarian-type stroma.

After the diagnosis, distal pancreatectomy and splenectomy were performed. Grossly, there was a 2.2 x 1.6 x 1.6 cm partially cystic well-circumscribed mass in the pancreatic tail containing thick clear fluid (Figure 8). Serial sections showed a 60% cystic and a 40% solid component. The mass showed no communication with the pancreatic ductal system.

Microscopic pictures of the resection are shown in Figures 9 – 11. The histologic examination revealed multiple cysts lined by a single layer of cuboidal cells that lacked mucin and had abundant eosinophilic cytoplasm. A prominent densely packed spindle cell-rich stroma was identified. The spindle cells had elongated nuclei with fine chromatin and inconspicuous nucleoli. No malignant features were present.

Pancreatic mucinous/non-mucinous cystic neoplasm (MCN) is an epithelial tumor typically associated with ovarian-type stroma. The majority of these lesions are found in the body or tail of the pancreas, occur in women, and have a mean age at diagnosis of 48 years old (1). Clinically, patients with MCN present with abdominal discomfort or epigastric pain, while others may be asymptomatic, and the tumor is found incidentally (2).

The histogenesis of these lesions is still in debate. Some proposed hypotheses suggest that the mesenchymal component derives from ectopic ovarian stroma incorporated during embryogenesis in the pancreas or represents persistent fetal periductal mesenchyme under hormonal stimulation (1).

Grossly, MCN usually presents with large unilocular or multilocular cysts, filled with thick gelatinous material, and lacks communication between the cyst and the pancreatic ductal system (3). Microscopically, the cysts are lined by mucin-producing columnar cells with varying degrees of cytologic and architectural atypia. However, cuboidal cells with no mucin can also occur. Based on the level of atypia, MCNs are further categorized as MCN with low- or high-grade dysplasia. The stromal component, called “ovarian-type stroma,” forms bands of densely packed spindle cells amongst the cysts, and its presence is required for the diagnosis. Typically, the stroma represents a smaller constituent of the lesion, and in some cases, it is difficult to identify as it can become hypocellular and replaced by hyalinized tissue (3). The epithelial cells stain positive with CK7 and MUC5AC. The ovarian-type stroma expresses PR (60-90%), ER (30%), SMA, and desmin. Luteinized cells can stain for inhibin and calretinin (1).

Molecularly, most MCN epitheliums carry activating mutations in codon 12 of KRAS (50-66%), some can carry loss-of-function mutations in RNF43 (1).

The case reported here has a very unusual presentation, given the fact that the stroma represents the predominant component of the lesion. The subepithelial stroma in this lesion was cellular and composed of cytologically bland spindle cells mimicking ovarian-type stroma without any malignant features. To our knowledge, this rare presentation of MCN has only been reported twice in the literature (4-5).

Molecular studies have shown frequent mutations in ID3, ARID1A, APC, and CDKN2A tumor suppressor genes in ACC (5-7). TP53 mutation or deletion has been identified in 12-24% of ACC (5,6). About 23% of ACC harbor gene fusion involving BRAF and RAF1 with the most common fusions being SND1-BRAF and HERPUD1-BRAF (5). These tumors are more sensitive to MEK inhibitors. In addition, microsatellite instability has been found in 8-14% of ACC (8,9).

Differential diagnosis:

The specimen was composed predominantly of bland-looking stroma on the initial biopsy, lacking a prominent epithelial component. Hence the initial differential diagnosis of this case comprises MCNs with sarcomatous stroma, carcinosarcoma, and benign mesenchymal tumors.

MCNs with sarcomatous stroma are infrequent and have been reported more frequently in the tail of the pancreas (6). The sarcomatous component is hypercellular, contains mitotic figures, and shows atypia and pleomorphism, in contrast with the bland looking stroma of the typical MCN.

Carcinosarcoma of the pancreas is a neoplasm composed of malignant mixed epithelial and mesenchymal elements (7). The sarcomatous component is composed of highly cellular areas with pleomorphic spindle cells containing abundant cytoplasm, hyperchromatic nuclei, and prominent nucleoli. Occasional bizarre cells can be identified. The histogenesis of this tumor remains unclear.

Benign mesenchymal tumors of the pancreas are extremely rare; some examples include inflammatory myofibroblastic tumor, extra gastrointestinal stromal tumor (GIST), schwannoma, and solitary fibrous tumor (SFT). Very few cases of pancreatic SFT have been reported in the literature. In the present case, the stroma did not show prominent staghorn-like vascularization, or a short storiform arrangement of the spindle cells, characteristics of SFT (8). Inflammatory myofibroblastic tumors could also be excluded based on the absence of a significant chronic inflammatory cell component. Primary GIST of the pancreas has been reported, showing the typical morphologic characteristics of the uniform spindle or epithelioid cells arranged in short fascicles or whorls (9). Differential diagnosis between MCN stroma and these mesenchymal tumors is based on histology and immunohistochemistry findings. The immunoprofile of the ovarian-type stroma of MCNs, showing positivity for inhibin, calretinin, estrogen and progesterone receptors, is not shared by these benign mesenchymal lesions. GIST is positive for c-kit and DOG1, schwannoma for S100, and SFT for STAT6 and CD34.

Finally, in the resection specimen, intraductal papillary mucinous neoplasms (IPMNs) should be considered in the differential diagnosis. IPMNs are characterized by cystic dilatation of pancreatic ducts in which an intraductal proliferation of neoplastic mucin-producing cells is arranged in a papillary pattern. IPMNs do not contain the ovarian-type stroma that characterizes the MCN (10).

References:

1. Basturk O, Esposito I, Fukushima N et al. Pancreatic mucinous cystic neoplasm. In: Board WCoTE, ed. WHO Classification of Tumours: Digestive System Tumours. 5th ed. Lyon, France: IARC Press; 2019:319-321.
2. Fukushima N, Fukayama M. Mucinous cystic neoplasms of the pancreas: pathology and molecular genetics. J Hepatobiliary Pancreat Surg. 2007;14(3):238-42.
3. Jang KT, Park SM, Basturk O, Bagci P, Bandyopadhyay S, Stelow EB, Walters DM, Choi DW, Choi SH, Heo JS, Sarmiento JM, Reid MD, Adsay V. Clinicopathologic characteristics of 29 invasive carcinomas arising in 178 pancreatic mucinous cystic neoplasms with ovarian-type stroma: implications for management and prognosis. Am J Surg Pathol. 2015;39(2):179-87.
4. Handra-Luca A, Couvelard A, Sauvanet A, Fléjou JF, Degott C. Mucinous cystadenoma with mesenchymal over-growth: a new variant among pancreatic mucinous cystadenomas? Virchows Arch. 2004;445(2):203-
5. Lee WA. Mucinous cystadenoma of the pancreas with predominant stroma creating a solid tumor. World J Surg Oncol. 2005; 3:59.
6. Van den Berg W, Tascilar M, Offerhaus GJ, Albores-Saavedra J, Wenig BM, Hruban RH, Gabrielson E. Pancreatic mucinous cystic neoplasms with sarcomatous stroma: molecular evidence for monoclonal origin with subsequent divergence of the epithelial and sarcomatous components. Mod Pathol. 2000;13(1):86-91.
7. Farbod Darvishian, James Sullivan, Saul Teichberg, Kevin Basham; Carcinosarcoma of the Pancreas: A Case Report and Review of the Literature. Arch Pathol Lab Med. 2002; 126 (9):1114–1117.
8. Baxter AR, Newman E, Hajdu CH. Solitary fibrous tumor of the pancreas. J Surg Case Rep. 2015; (12): rjv144.
9. Trabelsi A, Yacoub-Abid LB, Mtimet A, et al. Gastrointestinal stromal tumor of the pancreas: A case report and review of the literature. N Am J Med Sci. 2009;1(6):324-326.
10. Basturk O, Esposito I, Fukushima N et al. Pancreatic intraductal papillary mucinous neoplasm. In: Board WCoTE, ed. WHO Classification of Tumours: Digestive System Tumours. Lyon, France: IARC Press; 2019:310-314.

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Case contributed by:

Julia A. Gallardo, M.D.

Sadhna Dhingra, M.D.

Department of Pathology and Immunology, Baylor College of Medicine

Conflict of Interest: NO

Answer: Acinar cell carcinoma

Final diagnosis:  

Acinar cell carcinoma

Educational Objectives and Discussion:

Educational Objectives

1.  Know the key histologic and immunohistochemical findings required for a diagnosis of acinar cell carcinoma.
2.  Recognize the most common gross findings and clinical presentation of acinar cell carcinoma.
3. Review the differential diagnosis and necessary workup to exclude histologically similar tumors.

Discussion

Acinar cell carcinoma (ACC) accounts for about 1-2 % of adult pancreatic neoplasms. The average age of adult patients is approximately 60 years. Some patients develop lipase hypersecretion and associated paraneoplastic syndrome. These tumors are generally well-circumscribed, at least partially encapsulated, solid, and large (average diameter 8-10 cm) with a homogenous pink to tan cut surface. They can arise in any part of the pancreas and are more common in the head region.

Microscopically, these tumors are typically denselycellular with minimal stroma. They may have different architectural patterns, solid and acinar patterns being the most prevalent. Less common patterns include a glandular and trabecular pattern. Individual tumor cells have striking eosinophilic cytoplasm, uniform nuclei, and a characteristic large central nucleolus. The mitotic rate is variable, ranging from 5 to 20 (mean 14) per 10 high power fields. Vascular invasion within the capsule of the neoplasm is common. The eosinophilic cytoplasm reflects the presence of cytoplasmic zymogen granules. However, in some cases, the cytoplasmic granularity is not well developed, and special stains are required to document their presence.

A cystic variant of ACC has been described as typically large, circumscribed tumors with cysts lined by single or multiple layers of neoplastic acinar cells. In these cystic lesions, there are areas of solid nests of acinar cells, areas of necrosis, and mitotic figures, which support a malignant process.

The finding of granular Periodic Acid-Schiff (PAS)/diastase positivity in the apical cytoplasm may be enough to confirm a diagnosis of acinar cell carcinoma (Figure 7). The butyrate esterase stain detects the presence of enzymatically active lipase in the neoplastic cells and is highly specific for acinar differentiation. Trypsin (Figure 8), chymotrypsin, and BCL10 (clone 331.1) (Figure 9) antibodies are the most sensitive, and simultaneous use of any two of them allows the detection of nearly 100% of acinar cell carcinomas. Of these, BCL10 is the most sensitive and specific. They have a favorable prognosis compared to the more common pancreatic ductal adenocarcinoma. (1-4)

Molecular studies have shown frequent mutations in ID3, ARID1A, APC, and CDKN2A tumor suppressor genes in ACC (5-7). TP53 mutation or deletion has been identified in 12-24% of ACC (5,6). About 23% of ACC harbor gene fusion involving BRAF and RAF1 with the most common fusions being SND1-BRAF and HERPUD1-BRAF (5). These tumors are more sensitive to MEK inhibitors. In addition, microsatellite instability has been found in 8-14% of ACC (8,9).

Differential diagnosis:

Well-differentiated pancreatic neuroendocrine tumor, previously called islet cell tumors/islet cell carcinomas, are the pancreatic counterparts of APUDomas (Amine Precursor Uptake and Decarboxylation tumors) or carcinoids. They can be functional or non-functional (more common), are composed of monotonous cells with typical coarse nuclear chromatin, and express general markers of neuroendocrine differentiation (diffuse/intense synaptophysin and usually also chromogranin staining). They are the most important differential diagnosis of acinar cell carcinoma. Similarities between the two include a solid, acinar, or glandular architecture, relatively minimal stroma, and nuclear uniformity. Features favoring the diagnosis of well-differentiated pancreatic neuroendocrine tumor include hyalinized or amyloid-like stroma between nests of neoplastic cells (indicative of insulinoma), trabecular or gyriform growth patterns (particularly when arranged in single cell-thick cords), central nuclear localization, a coarsely clumped “salt and pepper” chromatin pattern, paler cytoplasm with less granularity and diffuse rather than focal positivity for synaptophysin and chromogranin. (1,10)

Mixed acinar-neuroendocrine carcinomas are malignant epithelial neoplasms with both acinar and neuroendocrine differentiation. They are defined as having > 30% of each line of differentiation by immunohistochemistry. They are best regarded as a subtype of acinar cell carcinoma because they share its clinical behavior and genomic features. (1,10)

Mixed acinar-ductal carcinomas are malignant epithelial neoplasms with both acinar and ductal differentiation. They are defined as having > 30% of each line by immunohistochemistry. These tumors may present with extensive extracellular colloid-like pools of mucin or nests of columnar or signet ring cells with cytoplasmic mucin or individual gland pattern of infiltration with an associated desmoplastic stromal response. Ductal differentiation is based on immunohistochemical reactivity for glycoproteins such as CEA (using monoclonal antibodies), CA19-9, or B72.3. Treatment is like that of ACC. (1,11)

Pancreatoblastomas are malignant epithelial neoplasms of the pancreas, principally affecting children in the first decade of life. However, it can rarely occur in adults. These are very cellular tumors and typically have more prominent lobules separated by cellular stromal bands. They are predominantly composed of solid sheets and acini of uniform cells with characteristic squamoid nests or corpuscles. Lesser amounts of a neuroendocrine component, ductal component, and/or primitive round blue cell component may be seen. Though acinar differentiation is the most common and predominant pattern in most cases, careful microscopic examination and additional sampling may help reveal ductal and/or neuroendocrine components as well as squamoid nests and cellular stromal bands. The age of the patient helps suggest the right diagnosis as pancreatoblastoma. (1)

Solid pseudopapillary neoplasm (SPN) are low grade malignant pancreatic tumors composed of poorly cohesive epithelial cells forming solid and pseudopapillary structures that lack a specific line of pancreatic epithelial differentiation. SPN displaying a predominantly solid growth pattern without foamy cells or eosinophilic globules could be confused with ACC. However, SPN never exhibits true lumen formation, so the presence of an acinar or glandular pattern would
exclude this entity. In contrast to ACC, SPN does not label with specific acinar markers (trypsin and chymotrypsin) and consistently shows diffuse nuclear β-catenin staining. (1,12)

References:

1. International Agency for Research on Cancer. (2019). WHO Classification of Tumours of the Digestive System. Lyon: International Agency for Research on Cancer.
2. Klimstra DS, Heffess CS, Oertel JE, Rosai J. Acinar Cell Carcinoma of the Pancreas. Am J Surg Pathol. 1992;16(9):815-837.
3. Wood LD, Klimstra DS. Pathology and Genetics of Pancreatic Neoplasms with Acinar Differentiation. Semin Diagn Pathol. 2014;31(6):491-497.
4. Matos JM, Schmidt CM, Turrini O, Agaram NP, Niedergethmann M, Saeger HD, Merchant N, Johnson CS, Lillemoe KD, Grützmann R. Pancreatic Acinar Cell Carcinoma: A Multi-institutional Study. J Gastrointest Surg. 2009;13(8):1495-502.
5. Chmielecki J, Hutchinson KE, Frampton GM, Chalmers ZR, Johnson A, Shi C, Elvin J, Ali SM, Ross JS, Basturk O, Balasubramanian S, Lipson D, Yelensky R, Pao W, Miller VA, Klimstra DS, Stephens PJ. Comprehensive genomic profiling of pancreatic acinar cell carcinomas identifies recurrent RAF fusions and frequent inactivation of DNA repair genes. Cancer Discov. 2014;4(12):1398-405.
6. Jiao Y, Yonescu R, Offerhaus GJ, Klimstra DS, Maitra A, Eshleman JR, Herman JG, Poh W, Pelosof L, Wolfgang CL, Vogelstein B, Kinzler KW, Hruban RH, Papadopoulos N, Wood LD. Whole-exome sequencing of pancreatic neoplasms with acinar differentiation. J Pathol. 2014;232(4):428-35.
7. Jäkel C, Bergmann F, Toth R, Assenov Y, van der Duin D, Strobel O, Hank T, Klöppel G, Dorrell C, Grompe M, Moss J, Dor Y, Schirmacher P, Plass C, Popanda O, Schmezer P. Genome-wide genetic and epigenetic analyses of pancreatic acinar cell carcinomas reveal aberrations in genome stability. Nat Commun. 2017;8(1):1323.
8. Liu W, Shia J, Gönen M, Lowery MA, O’Reilly EM, Klimstra DS. DNA mismatch repair abnormalities in acinar cell carcinoma of the pancreas: frequency and clinical significance. Pancreas. 2014;43(8):1264-70.
9. La Rosa S, Sessa F, Capella C. Acinar Cell Carcinoma of the Pancreas: Overview of Clinicopathologic Features and Insights into the Molecular Pathology. Front Med (Lausanne). 2015;2:41.
10. Ulich T, Cheng L, Lewin KJ. Acinar-endocrine cell tumor of the pancreas. Report of a pancreatic tumor containing both zymogen and neuroendocrine granules. Cancer. 1982;50(10):2099-105.
11. Stelow EB, Shaco-Levy R, Bao F, Garcia J, Klimstra DS. Pancreatic Acinar Cell Carcinomas with Prominent Ductal Differentiation: Mixed Acinar Ductal Carcinoma and Mixed Acinar Endocrine Ductal Carcinoma. Am J Surg Pathol. 2010;34(4):510-8.
12. Notohara, Kenji, Hamazaki, Shuji, Tsukayama, Choutatsu, et al. Solid-Pseudopapillary Tumor of the Pancreas: Immunohistochemical Localization of Neuroendocrine Markers and CD10. Am J Surg Pathol. 2000;24(10):1361-1371.

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Case contributed by:

Pragya Jain, MD

Saryn Doucette, MD

Department of Pathology and Laboratory Medicine
Medical College of Wisconsin

Conflict of Interest: NO

Answer: Pancreatic adenosquamous carcinoma with mucoepidermoid carcinoma-like features

Final diagnosis:  

Pancreatic adenosquamous carcinoma with mucoepidermoid carcinoma-like features

Educational Objectives and Discussion:

Educational Objectives

1. Review the clinicopathologic features of pancreatic adenosquamous carcinoma with mucoepidermoid carcinoma-like features
2. Understand the molecular alterations of pancreatic adenosquamous carcinoma with mucoepidermoid carcinoma-like features
3. Discuss pertinent differential diagnosis for pancreatic adenosquamous carcinoma with mucoepidermoid carcinoma-like features

Discussion

The current tumor demonstrated that tumor cells were positive for pan-cytokeratin. p40, p63, and CK5 highlighted epidermoid tumor cells. CDX2 and CK20 highlighted luminal cells and mucin-producing cells. Synaptophysin, chromogranin, and CD56 stains were negative. Intracytoplasmic and luminal mucinous secretions were highlighted by mucicarmine stain (Figures 5-7). Molecular study showed mutations in KRAS, CDKN2A, SF3B1, and TP53 genes.

Pancreatic mucoepidermoid carcinoma (PAN-MEC, more appropriately termed as pancreatic adenosquamous carcinoma with mucoepidermoid carcinoma-like features) has been proposed as one of the histologic subtypes of pancreatic adenosquamous carcinoma because of their
clinicopathologic and molecular similarities (1). To date, approximately 20 PAN-MEC cases have been documented (1-6). This tumor is more frequently located at the pancreatic body/tail and is significantly larger in size and more aggressive than those of the conventional pancreatic ductal adenocarcinomas (1). 

Similar to salivary gland MECs, three intermingled cell types, including mucin-producing cells, epidermoid cells, and intermediate cells, are usually present in varying proportions in PAN-MEC. Mucin-producing cells (mucocytes) produce mucin (and are positive for mucin stains such as mucicarmine). These cells may have a vacuolated, columnar, or goblet cell-like appearance (Figure 8). Mucocytes often form the lining of microcysts or duct-like structures.

Epidermoid cells are polygonal and squamoid in appearance with dense eosinophilic cytoplasm, which can be highlighted by immunohistochemical stains such as p40, p63, or CK5/6. Epidermoid cells commonly have nested, or sheet-like growth pattern and are often located at the periphery of the nests or cribriform/microcystic structures. While intercellular bridges may be found, keratin pearl formation, overt keratinization, or dyskeratosis is not typically seen. Intermediate cells are less differentiated, and are morphologically not mucous or fully epidermoid cells. Their appearance may vary from small clear cells to small basaloid cells with scant basophilic cytoplasm or intermediate oval cells with pale eosinophilic cytoplasm. The intermediate cells are often admixed with epidermoid cells or mucocytes (Figure 9).

Despite morphologic similarity, PAN-MEC appears not to be a counterpart of MEC of the salivary gland. In the salivary gland, a high proportion of MECs have been reported to harbor an oncogenic CRTC1/3–MAML2 gene fusion; whereas in the pancreas, these gene fusions were not detected by PCR in a study involving 16 PAN-MEC cases (all cases were classified as high-grade based on the salivary gland MEC grading system) (1). In addition, PAN-MEC has been reported to harbor KRAS and TP53 mutation, which is similar to the most common molecular signature found in pancreatic ductal adenocarcinomas (4)

Differential diagnosis:

Due to morphologic similarity, metastatic mucoepidermoid carcinoma or clear cell carcinoma of the salivary gland should be one of the first differentials to consider. However, the lack of clinical history of a salivary gland tumor, the presence of a pancreatic precursor lesion (high grade pancreatic intraepithelial neoplasia), and a component of conventional  invasive ductal adenocarcinoma would support this tumor being a primary pancreatic carcinoma with MEC features as opposed to a metastasis from salivary gland. Goblet cells and microcystic structures are generally not seen in clear cell carcinoma of the salivary gland, although squamous differentiation and mucinproduction are not uncommon (7).

Conventional pancreatic adenosquamous carcinoma is also in the differential diagnosis. By definition, this tumor has at least a 30% squamous cell carcinoma component with coexisting ductal adenocarcinoma. Apparent keratinization and squamous pearl formation, as well as focal nuclear anaplasia, are often noted. Low-grade mucoepidermoid carcinoma-like features are generally absent.

Neoadjuvant therapy has been reported to induce squamous metaplasia of ductal columnar cells. However, there was no squamous metaplasia identified in the background pancreatic tissue of the present case. Although focal squamous transdifferentiation from the small ductal adenocarcinoma component induced by neoadjuvant therapy (8) cannot be completely excluded, the diffuse squamoid cells intermingled with other cell types and predominant cribriform/microcystic architecture are difficult to be explained by focal squamous transdifferentiation changes.

Pancreatoblastoma is an uncommon malignant epithelial neoplasm characterized by multilineage differentiation including at least prominent acinar differentiation and focal squamoid morules that exhibit nuclear beta-catenin immunopositivity. Tumors are commonly seen in children but can occur in adults. Ductal/glandular or neuroendocrine differentiation can also be seen but are generally focal (9-10).

References:

1. Saeki K, Ohishi Y, Matsuda R, et al. “Pancreatic Mucoepidermoid Carcinoma” Is not a Pancreatic Counterpart of CRTC1/3-MAML2 Fusion Gene-related Mucoepidermoid Carcinoma of the Salivary Gland, and May More Appropriately be Termed Pancreatic Adenosquamous Carcinoma With Mucoepidermoid Carcinoma-like Features. Am J Surg Pathol. 2018;42:1419-1428.
2. Onoda N, Kang SM, Sugano S, Yamashita Y, Chung YS, Sowa M. Mucoepidermoid carcinoma of the pancreas: report of a case. Surgery. 1995;25:843-847.
3. Ma R, Yu YQ, Li JT, Peng SY. Mucoepidermoid carcinoma of the pancreas: a case report and a review of literature. Journal of research in medical sciences: the official journal of Isfahan University of Medical Sciences. 2012;17:886-889.
4. Kardon DE, Thompson LD, Przygodzki RM, Heffess CS. Adenosquamous carcinoma of the pancreas: a clinicopathologic series of 25 cases. Mod Pathol. 2001;14:443-451.
5. Hu HJ, Zhou RX, Liu F, Wang JK, Li FY. You cannot miss it: Pancreatic mucoepidermoid carcinoma: A case report and literature. Medicine. 2018;97:e9990.
6. Boecker J, Feyerabend B, Tiemann K, et al. Adenosquamous Carcinoma of the Pancreas Comprise a Heterogeneous Group of Tumors With the Worst Outcome: A Clinicopathological Analysis of 25 Cases Identified in 562 Pancreatic Carcinomas Resected With Curative Intent. Pancreas. 2020;49:683-691.
7. Hsieh MS, Wang H, Lee YH, Ko JY, Chang YL. Reevaluation of MAML2 fusion-negative mucoepidermoid carcinoma: a subgroup being actually hyalinizing clear cell carcinoma of the salivary gland with EWSR1. Hum Pathol. 2017;61:9-18.
8. Marcus R, Maitra A, Roszik J. Recent advances in genomic profiling of adenosquamous carcinoma of the pancreas. The Journal of pathology. 2017;243:271-272.
9. Klimstra DS, Wenig BM, Adair CF, Heffess CS. Pancreatoblastoma. A clinicopathologic study and review of the literature. Am J Surg. 1995;19:1371-1389.
10. Tanaka Y, Kato K, Notohara K, et al. Significance of aberrant (cytoplasmic/nuclear) expression of beta-catenin in pancreatoblastoma. The Journal of pathology. 2003;199:185-190.

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Case contributed by:

Wei Zheng, Assistant Professor

Alyssa M. Krasinskas, Professor

Department of Pathology and Laboratory Medicine

Emory School of Medicine

Conflict of Interest: NO

Answer: Acinar cystic transformation of the pancreas

Final diagnosis:  

Acinar cystic transformation of the pancreas

Educational Objectives and Discussion:

Educational Objectives

1. To understand the clinicopathologic features of the acinar cystic transformation of the pancreas.
2. To understand the molecular alterations of the acinar cystic transformation of the pancreas.
3. To discuss the differential diagnoses of the acinar cystic transformation of the pancreas.

Discussion

Acinar cystic transformation of the pancreas, also called acinar cell cystadenoma, is currently considered a non-neoplastic cystic pancreatic lesion that is lined by benign-appearing acinar and ductal epithelium. These lesions can occur throughout the pancreas, but they are more common in the pancreatic head. Some examples may diffusely involve the entire organ. Acinar cystic transformation commonly occurs in adults (mean age 43 years old) and shows female predominance (F:M=3:1) (1-9). Clinically it can present as recognized macroscopic lesions or incidental microscopic lesions. Patients can present with abdominal pain, dyspepsia or palpable mass. Some cases are completely asymptomatic. The etiology is unknown, but some cases may be related to obstruction. The size of these lesions can range from 1.5 cm – 19.7 cm (mean 5.8 cm) and cysts may be unilocular or multilocular with a smooth cyst lining and rare communication with the main pancreatic duct.

Microscopically, acinar cystic transformation is characterized by cysts of variable sizes lined by bland cuboidal eosinophilic epithelium with both acinar and ductal differentiation, cytoplasmic zymogen rich granules and without significant nuclear atypia, mitotic figures, necrosis, or infiltrative growth pattern.

The apical zymogen granules stain positively for the periodic acid-Schiff (PAS) stain and are resistant to diastase (Figures 5 & 6). Immunohistochemical labeling for the pancreatic enzymes trypsin (Figure 7), chymotrypsin, and lipase is seen in the lining epithelial cells, and cytokeratins (such as cytokeratin 7) are also detectable in the lining epithelium.

Molecular studies have been done on a few cases with one showing chromosomal gains of 1p, 3p, 5q, 6p, 7q, 8, 10q, 11, 14, 20, and X by array comparative genomic hybridization (10). However, another study performed X-chromosome inactivation analysis on 5 cases and showed that these lesions have a random X-chromosome inactivation pattern (11), supporting a non-neoplastic process.

Differential diagnosis:

Serous cystadenoma of the pancreas is a benign epithelial cystic neoplasm that is composed of uniform cuboidal, glycogen-rich pale pink to clear cells that often form cysts containing serous fluid. Immediately underlying the clear epithelium is an interweaving network of capillaries that is challenging to see on H&E but can be highlighted by CD31 stain. A central scar can be present, which consists of hyalinized stroma. Owing to the presence of abundant intracytoplasmic glycogen, PAS staining is positive in tumor cells but PAS-D staining is negative. Serous epithelium is immunoreactive for inhibin and Glut-1.

Mucinous cystic neoplasm (MCN) is another differential that is also characterized by pancreatic cysts of the body/tail that do not communicate with pancreatic duct. Cysts are characteristically lined by mucinous/non-mucinous epithelium with underlying entity defining ovarian-type stroma. Acinar epithelial lining is not a feature of MCN.

Squamoid cysts of the pancreatic duct are not neoplastic and are lined by epithelium with squamous or transitional differentiation instead of acinar and ductal differentiation.

Acinar cell cystadenocarcinoma is exceedingly rare. The epithelium of acinar cell cystadenocarcinoma is more complex than that of acinar cystic transformation and the acinar cells are less well polarized, and show significant nuclear atypia, including pleomorphism and prominent nucleoli. Areas of necrosis, solid nests of neoplastic cells, easily identifiable mitoses, and infiltration into the surrounding stroma support a malignant diagnosis.

References:

1. Zamboni G, Terris B, Scarpa A, et al. Acinar Cell Cystadenoma of
the Pancreas: A New Entity? Am J Surg Pathol. 2002, 26(6): 698-704.
2. Albores-Saavedra J. Acinar Cystadenoma of the Pancreas: A
Previously Undescribed Tumor. Ann Diagn Pathol. 2002, 6(2): 113-5.
3. Chatelain D, Paye F, Mourra N, et al. Unilocular Acinar Cell
Cystadenoma of the Pancreas an Unusual Acinar Cell Tumor. Am J Clin
Pathol. 2002, 118(2): 211-4.
4. G Klöppel. Pseudocysts and Other Non-Neoplastic Cysts of the
Pancreas. Semin Diagn Pathol. 2000 Feb; 17(1); 7-15.
5. McEvoy MP, Rich B, Klimstra D, et al. Acinar Cell Cystadenoma of
the Pancreas in a 9-year-old Boy. J Pediatr Surg. 2010, 45(5): e7-9.
6. Wolf AM , Shirley LA, Winter JM, et al. Acinar Cell Cystadenoma of
the Pancreas: Report of Three Cases and Literature Review. J
Gastrointest Surg. 2013l,17(7): 1322-6.
7. Singhi AD, Norwood S, Liu TC, et al. Acinar Cell Cystadenoma of the
Pancreas: A Benign Neoplasm or Non-Neoplastic Ballooning of Acinar and
Ductal Epithelium. Am J Surg Pathol. 2013, 37(9): 1329-35.
8. Wang G, Ji L, Qu FZ, et al. Acinar Cell Cystadenoma of the
Pancreas: A Retrospective Analysis of Ten-Year Experience From a
Single Academic Institution. Pancreatology, 2016, 16(4): 625-31.
9. Zhang X, Zhu H, Yang X, et al. Post-obstructive Cyst Formation in
Pancreas and Cystic Acinar Transformation: Are They Same? Pathol Res
Pract 2017, 213(8): 997-1001.
10. Khor TS, Badizadegan K, Ferrone C, et al. Acinar cystadenoma of
the pancreas: a clinicopathologic study of 10 cases including
multilocular lesions with mural nodules. Am J Surg Pathol.
2012;36(11):1579‐1591.
11. Singhi AD, Norwood S, Liu TC, et al. Acinar cell cystadenoma of
the pancreas: a benign neoplasm or non-neoplastic ballooning of acinar
and ductal epithelium? Am J Surg Pathol. 2013;37(9):1329‐1335.

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Case contributed by:

Yue Xue, MD, PhD

Rebecca C. Obeng, MD, PhD

Department of Pathology and Laboratory Medicine

Northwestern University, Chicago, IL 60611, USA

Conflict of Interest: NO

Answer: Undifferentiated carcinoma, sarcomatoid type with rhabdoid features

Microscopic description:
The tumor had a predominantly solid architecture and was primarily composed of loosely cohesive sheets of large ovoid-to-polygonal tumor cells. Focal glandular architecture was also seen. The tumor cells had large atypical vesicular nuclei, prominent nucleoli, and
eosinophilic to amphophilic cytoplasm with abundant intracytoplasmic eosinophilic globules, which displaced the tumor nuclei peripherally, creating a rhabdoid appearance. Multifocal lymphovascular and perineural invasion, abnormal mitoses, and areas of necrosis were also present.

Immunohistochemistry and special stains:
The tumor cells were positive for pancytokeratin (AE1/AE3), vimentin, and EMA. Ki-67 immunostain was positive in 60% of tumor cells. Intracytoplasmic eosinophilic globules were positive for PAS and were resistant to diastase digestion. Tumor cells showed diffuse loss of INI1 immunostain not only in solid areas, but also in areas of glandular differentiation. The tumor cells were negative for CK7, CD10, synaptophysin, chromogranin, and CD34.

Molecular analysis:
SMARCB1 gene mutation was detected.

Final diagnosis:  

Undifferentiated carcinoma, sarcomatoid type with rhabdoid features

Educational Objectives and Discussion:

Educational Objectives
1. Review undifferentiated carcinoma of pancreas and its subtypes

2. Discuss the clinicopathologic features of a recently described entity, pancreatic undifferentiated rhabdoid carcinoma

3. Understand pertinent differential diagnosis for undifferentiated carcinoma, sarcomatoid type with rhabdoid features

Discussion

Undifferentiated carcinoma is one of the histologic subtypes of pancreatic ductal adenocarcinoma. Tumors are usually hypercellular and composed of poorly cohesive tumor cells which often coexpress cytokeratin and vimentin. Osteoclast-like giant cells are typically lacking. Perineural and vascular invasion are also frequent findings. The current (5^th) edition of WHO Classification of Tumors (Digestive System Tumors) recognizes three subtypes of undifferentiated carcinoma based on the tumor’s morphological patterns. These include anaplastic, sarcomatoid, and carcinosarcoma (1).

Sarcomatoid type undifferentiated carcinoma is composed of poorly cohesive atypical spindle-shaped tumor cells resembling a sarcoma. Tumors may contain admixed heterologous elements including bone and cartilage. At least 80% of the tumor typically shows spindle cells, with or without heterologous differentiation (1). A more specific morphologic type of sarcomatoid undifferentiated carcinomas with rhabdoid features has also been described, as with the case illustrated here (2). These are composed of sheets of dishesive rhabdoid cells with myxoid stroma. Pleomorphic giant cells, spindling and tubular components may also be seen and loss of nuclear positivity for SMARCB1 (INI1) is characteristic. SMARCB1/INI1 is known to encode for a tumor suppressor gene located on chromosomal band 22q11.2 (3, 4), and is a core subunit of a group of chromatin-modeling complexes, the SWI/SNF family. Biallelic inactivation of this gene is associated with highly malignant tumors with prominent rhabdoid morphology, including malignant rhabdoid tumor (both renal and “pure” extrarenal), atypical teratoid/rhabdoid tumor, epithelioid sarcoma and renal medullary carcinoma, among others. (3, 5, 6, 7).

Agaimy et al. recently described a group of pancreatic undifferentiated carcinomas with prominent rhabdoid morphology, which they named pancreatic undifferentiated rhabdoid carcinoma (PURC) (8). The authors described 14 such cases from their home institution as well as an additional 46 cases discovered on review of the literature. There were 44 males and 16 females (male-to-female ratio=2.8:1) of mean age 65 years (range 30 -96 years). Patients had an extremely poor prognosis with 45 of 49 (92%) with available follow-up information reportedly dying of disease within 1-19 months.

Agaimy et al also described two distinct subtypes of pancreatic undifferentiated rhabdoid carcinoma based both on the histomorphologic features and molecular profiles. One subtype is the pleomorphic giant cell subtype which shows highly pleomorphic neoplastic cells with abundant eosinophilic cytoplasm frequently containing rhabdoid inclusions. Molecular studies have shown this particular subtype to have a strong association with KRAS alteration and intact SMARCB1 gene. The second subtype, which is similar to the current case, is the monomorphic anaplastic subtype. This subtype shows uniformly atypical rhabdoid cytological features without significant pleomorphism. The tumor cells in the monomorphic anaplastic subtype have medium to large vesicular nuclei, prominent nucleoli, and eosinophilic cytoplasm which frequently contains rhabdoid cytoplasmic inclusions. This subtype shows diffuse loss of SMARCB1 nuclear immunostain as well as SMARCB1 gene mutation. However, no KRAS alterations are detected in these tumors (8).

Figure-6.-INI1-immunohistochemical-stain-20X

Differential diagnosis:

The morphologic features of undifferentiated carcinoma, sarcomatoid type with rhabdoid features raises several differential diagnoses one of which is poorly differentiated neuroendocrine carcinoma, particularly the large cell variant. The large cell variant of neuroendocrine carcinoma is often composed of round to polygonal cells which can have vesicular nuclei and prominent nucleoli. Glandular differentiation can rarely be present. However, unlike pancreatic undifferentiated carcinomas with rhabdoid morphology neuroendocrine carcinoma almost always expresses at least one neuroendocrine marker (synaptophysin and chromogranin) and shows intact INI1 (9).

Solid pseudopapillary neoplasm (SPN) is another differential to consider. The presence of a pancreatic neoplasm in a female in her 20’s should always raise the possibility of SPN as a
differential diagnosis. The presence of PAS-positive and diastase resistant intracytoplasmic globules is also characteristic of SPN. However, SPN often has a “pseudo-papillary” morphology, with nuclear beta-catenin labeling and is negative or focally positive for cytokeratin (1,10).

Melanomas can also display rhabdoid morphology, and can lose HMB45 and Melan-A expression. However, melanoma with rhabdoid morphology is often is positive for S100, shows intact INI1 staining and is cytokeratin negative (11).

Proximal-type epithelioid sarcoma is another neoplasm that can have predominant rhabdoid features with negative INI1 staining/INI1 loss. Differentiating undifferentiated carcinoma with rhabdoid features and SMARCB1 (INI1) loss from proximal-type epithelioid sarcoma can be very difficult. However, the presence of glandular architecture in this case makes this entity less likely. CD34 immunostain is positive in approximately 50% of epithelioid sarcoma (8,12).

References:

1.WHO Classification of Tumours Editorial Board, World Health Organization., International Agency for Research on Cancer. Digestive system tumours. 5th ed. Lyon: IARC Press; 2019.
2. Alguacil-Garcia A, Weiland LH. The histologic spectrum, prognosis, and histogenesis of the sarcomatoid carcinoma of the pancreas. Cancer 1977;39:1181-1189.
3. Kohashi K, Oda Y. Oncogenic roles of SMARCB1/INI1 and its deficient tumors. Cancer Sci. 2017;108(4):547-552.
4. Cho YM, Choi J, Lee OJ, et al. SMARCB1/INI1 missense mutation in mucinous carcinoma with rhabdoid features. Pathol Int 2006;56:702-706.
5.Fuller CE. All things rhabdoid and SMARC: An enigmatic exploration with Dr. Louis P. Dehner. Semin Diagn Pathol. 2016;33(6):427‐440.
6. Donner LR, Wainwright LM, Zhang F, et al. mutation of the INI1 gene in composite rhabdoid tumor of the endometrium. Hum Pathol 2007;38:935–939.
7. Fuller CE, Pfeifer J, Humphrey P, et al. Chromosome 22q dosage in composite extrarenal rhabdoid tumors:clonal evolution or a phenotypic mimic? HumPathol 2001;32:1102–8.
8. Agaimy A, Haller F, Frohnauer J, et al. Pancreatic undifferentiated rhabdoid carcinoma: KRAS alterations and SMARCB1 expression status define two subtypes. Mod Pathol. 2015;28(2):248‐260.
9. Basturk O, Tang L, Hruban RH, et al. Poorly differentiated neuroendocrine carcinomas of the pancreas: a clinicopathologic analysis of 44 cases. Am J Surg Pathol. 2014;38(4):437‐447.
10. Odze RD, Goldblum JR. Odze and Goldblum surgical pathology of the GI tract, liver, biliary tract, and pancreas. Third edition. ed. Philadelphia, PA: Saunders/Elsevier; 2015:xix, 1612 pages.
11. Abbott JJ, Amirkhan RH, Hoang MP. Malignant Melanoma With a Rhabdoid Phenotype: Histologic, Immunohistochemical, and Ultrastructural Study of a Case and Review of the Literature. Arch Pathol Lab Med. 2004;128(6):686-8
12. Sullivan LM, Folpe AL, Pawel BR, et al. Epithelioid sarcoma is associated with a high percentage of SMARCB1 deletions. Mod Pathol 2013;26:385-392.

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Case contributed by:

Aaron Sohn, M.D.
Anatomic and Clinical Pathology Resident, PGY-4
Baylor University Medical Center, Dallas, TX

Atin Agarwal, M.D.
Staff Pathologist
Baylor University Medical Center, Dallas, TX

Conflict of Interest: NO

Answer: Undifferentiated carcinoma, anaplastic type

Microscopic appearance: 
This is a high-grade malignancy revealing predominantly diffuse sheet-like growth pattern, without overt glandular differentiation, with hemorrhage and necrosis. It is composed of atypical epithelioid and spindle-shaped cells intermixed with pleomorphic, multinucleated cells with bizarre nuclei.

Immunohistochemistry: 
These cells are positive for pancytokeratin, CK7, Cam 5.2, EMA (focal), CK5/6, and p63 immunohistochemical stains.

Final diagnosis:  
Undifferentiated carcinoma, anaplastic type

 Discussion:
Undifferentiated carcinoma is one of the histologic subtypes of pancreatic ductal adenocarcinoma. Three morphological patterns of this subtype have been recognized by the current (5^th edition) WHO.

Anaplastic type undifferentiated carcinoma is characterized by pleomorphic mononuclear cells admixed with bizarre-appearing giant cells with eosinophilic cytoplasm. At least 80% of the neoplasm consists of solid sheets of cells lacking gland formation and showing markedly pleomorphic nuclei. There is usually a neutrophilic inflammatory infiltrate. Keratin expression is typically present.

Sarcomatoid type undifferentiated carcinoma is characterized by spindle-shaped cells and may contain admixed heterologous elements of bone and cartilage. At least 80% of the neoplasm displays spindle cell features,with or without heterologous differentiation. A potential pitfall exists if only heterologous elements are sampled in a limited biopsy specimen, suggesting a soft tissue tumor, chondrosarcoma, or osteosarcoma. Sarcomatoid undifferentiated carcinomas with rhabdoid cells have also been described. Loss of nuclear expression of SMARC1 (INI1) is characteristic in these rare cases.

Carcinosarcoma reveals components with obvious epithelial morphology and sarcomatous elements, with or without heterologous differentiation, and requires each component to constitute 30% of the neoplasm.

Differential diagnosis:

• Metastatic Melanoma to the small intestine is well documented and may histologically mimic undifferentiated carcinoma, anaplastic type. Morphologically, melanoma may show large pleomorphic cells with eosinophilic cytoplasm and macronuclei admixed with spindle or epithelioid cells. A panel of routine melanoma immunohistochemistry including Melan-A, HMB45, S100, and SOX10 is highly sensitive for metastatic melanoma.
• Undifferentiated carcinoma with osteoclast-like giant cells, another histologic subtype of pancreatic ductal adenocarcinoma, is composed of neoplastic mononuclear cells, mononuclear histiocytic cells, and non-neoplastic osteoclast-like multinucleated giant cells. Heterologous elements such as bone and cartilage may be present.
• Dedifferentiated GISTs are composed atypical spindle-shaped, epithelioid cells, and may contain large pleomorphic cells. These neoplasms are exceptionally rare and more frequently observed in patients with a history of GIST following long term tyrosine kinase inhibitor therapy. Notably, dedifferentiation typically includes a loss of KIT immunoreactivity.
• Adenosquamous carcinoma of the pancreas comprises approximately 2% of pancreatic exocrine cancers. Squamous and glandular components may be intermixed or distinctly separate. The squamous component must comprise at least 30% of the tumor and will stain with p63, CK5/6, and high molecular weight cytokeratin.

References:

1. Gulati A, Kaushal V, Gupta N. Undifferentiated carcinoma of pancreas with osteoclast-like giant cells mimicking a pseudopancreatic cyst. J Cancer Res Ther. 2015;11(4):1046.
2. Hoorens A, Prenzel K, Lemoine NR, Klöppel G. Undifferentiated carcinoma of the pancreas: analysis of intermediate filament profile and Ki-ras mutations provides evidence of a ductal origin. J Pathol. 1998;185(1):53-60.
3. Manduch M, Dexter DF, Jalink DW, Vanner SJ, Hurlbut DJ. Undifferentiated pancreatic carcinoma with osteoclast-like giant cells: report of a case with osteochondroid differentiation. Pathol Res Pract. 2009;205(5):353-9.
4. Yonemasu H, Takashima M, Nishiyama KI et al. Phenotypical characteristics of undifferentiated carcinoma of the pancreas: a comparison with pancreatic ductal adenocarcinoma and relevance of E-cadherin, alpha catenin and beta catenin expression. Oncol Rep. 2001;8(4):745-52.
5. Patil DT, Rubin BP. Gastrointestinal stromal tumor: advances in diagnosis and management. Arch Pathol Lab Med. 2011;135(10):1298-310.
6. Odze RD, Goldblum JR. Odze and Goldblum surgical pathology of the GI tract, liver, biliary tract, and pancreas. Third edition. ed. Philadelphia, PA: Saunders/Elsevier; 2015:xix, 1612 pages.
7. WHO Classification of Tumours Editorial Board, World Health Organization., International Agency for Research on Cancer. Digestive system tumours. 5th ed. Lyon: IARC Press; 2019
8. Choi JJ, Sinada-Bottros L, Maker AV, Weisenberg E. Dedifferentiated gastrointestinal stromal tumor arising de novo from the small intestine. Pathol Res Pract. 2014;210(4):264-6.
9. Oka K, Inoue K, Sugino S et al. Anaplastic carcinoma of the pancreas diagnosed by endoscopic ultrasound-guided fine-needle aspiration: a case report and review of the literature. J Med Case Rep. 2018;12(1):152.
10. Sano M, Homma T, Hayashi E, Noda H, Amano Y, Tsujimura R, Yamada T, Quattrochi B, Nemoto N.Clinicopathological characteristics of anaplastic carcinoma of the pancreas with rhabdoid features. Virchows Arch. 2014;465(5):531-8.
11. Muraki T, ReidMD, Basturk O, Jang KT, Bedolla G, Bagci P, Mittal P, Memis B, Katabi N, Bandyopadhyay S, Sarmiento JM, Krasinskas A, Klimstra DS, Adsay Undifferentiated Carcinoma with Osteoclastic Giant Cells of the Pancreas: Clinicopathologic Analysis of 38 Cases Highlights a More Protracted Clinical Course Than Currently Appreciated. Am J Surg Pathol. 2016;40(9):1203-16. 
12. Agaimy A, Haller F, Frohnauer J, Schaefer IM, Ströbel P, Hartmann A, Stoehr R, Klöppel G. Pancreatic undifferentiated rhabdoid carcinoma: KRAS alterations and SMARCB1 expression status define two subtypes.Mod Pathol. 2015;28(2):248-60. 

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Case contributed by:

Adam L. Booth, MD
Anatomic and Clinical Pathology Resident, PGY-4
University of Texas Medical Branch, Galveston, TX

Nicole D. Riddle, MD
Assistant Professor, Associate Residency Program Director
University of South Florida, Tampa, FL

Answer: Vasculitis-related cholangiopathy

Final diagnosis:  

Vasculitis-related cholangiopathy

Educational Objectives and Discussion:

Educational Objectives

1. Recognize important histologic features in the assessment of vasculitis and other inflammatory disorders of the biliary tree.
2. Understand the integration of histologic and laboratory evidence in generating a specific diagnosis.
3. Review the differential diagnosis and necessary workup for benign mimickers and inflammatory lesions of the biliary tree.

Discussion

Vasculitis of the biliary system is rare and can present as a component of systemic disease or as single organ involvement, although progression from single organ to systemic disease can occur. Injury to the biliary tree via vasculitis can result in ischemic cholangiopathy. As an acute insult, ischemic cholangiopathy is characterized by edema, necrosis, and sloughing of the biliary epithelium. A chronic course, as may be seen with vasculitis, results in fibrosis of the bile duct with the risk of eventual obliteration [1, 2].

Immunohistochemical staining was performed for this case. CD3 and CD20 stains showed a lymphocytic inflammatory infiltrate composed of a mixed B and T cell population. CD138, IgG, and IgG4 staining showed no increase in IgG4-positive plasma cells (result not shown).

Classification criteria for more common vasculitides were developed by the American College of Rheumatology (ACR) in 1990. The ACR classification criteria integrate clinical characteristics and histopathologic findings, and efforts to systematically update these criteria are ongoing. The current nomenclature of vasculitis is described in the 2012 Revised International Chapel Hill Consensus Conference Nomenclature of Vasculitides, which also describes some classification features. Vasculitis can be categorized as infectious vs. noninfectious. Noninfectious vasculitis can then be further subdivided by the type of vessel predominantly affected – small, medium, or large. The presence of immune complexes or autoantibodies further contributes to classification in combination with clinical features (patient age, site of involvement, etc) [3].

Among specific rheumatologic entities, biliary involvement is most frequently seen in polyarteritis nodosa, which typically affects medium-sized arteries with a necrotizing inflammatory process and has no ANCA association [4]. The ANCA-associated vasculitides including microscopic polyangiitis (small vessel involvement without granulomas) and eosinophilic granulomatosis with polyangiitis (small to medium vessel involvement) can affect the biliary system as a component of systemic disease [5, 6]. Vasculitis of the extrahepatic biliary tree has also been reported in association with hepatitis B, cryoglobulinemia (including hepatitis C associated), IgA vasculitis, Takayasu vasculitis, and giant cell arteritis [7, 8].

Differential diagnosis:

While a cholestatic pattern of injury with bile duct thickening raises clinical concern for a neoplastic process, the differential diagnosis includes several benign entities. Choledocholithiasis generally can be detected through radiographic and/or endoscopic studies, but an obstructing stone can occasionally be missed. Infectious causes include bacterial, parasitic (Ascaris lumbricoides, Clonorchis sinensis, Opisthorchis viverrini), and opportunistic/AIDS-related (Cryptosporidium parvum, cytomegalovirus) entities.

IgG4-associated cholangiopathy often presents with diffuse involvement of the biliary tree on imaging studies but can mimic primary sclerosing cholangitis with segmental involvement [9]. Key histologic features in IgG4-related disease include a dense lymphoplasmacytic infiltrate that may preferentially affect peribiliary glands compared to the lamina propria, along with storiform fibrosis, and obliterative phlebitis. Immunohistochemical staining for CD138, IgG, and IgG4 with an IgG4+:IgG+ plasma cell ratio >0.4 supports the pathologic diagnosis when observed in combination with typical histologic features [10].

Primary biliary cholangitis (PBC) typically presents as chronic cholestasis, and an antimitochondrial antibody is identified in 95% of cases. Histologically, PBC is characterized by chronic, nonnecrotizing granulomatous lesions primarily affecting the small, intrahepatic bile ducts, although florid duct lesions with necrosis can be seen. Ductular reaction and ductal epithelial cell injury can be seen in early stage PBC. Ductopenia, septal fibrosis, and even cirrhosis can be seen in late stage PBC [11]. Primary sclerosing cholangitis (PSC), in contrast, frequently involves both the intra- and extrahepatic ducts, classically demonstrating a beaded appearance on imaging, which represents alternating segments of stricture and uninvolved duct. Affected bile ducts show a characteristic onion skin pattern of fibrosis that may be associated with mild chronic inflammation and can ultimately result in duct obliteration.

Sarcoidosis frequently involves the liver, and variable involvement of the extrahepatic biliary tree has been reported. The lesions can cause compressive cholestasis when arising along the biliary tree, thereby mimicking PSC [12]. Well-formed non-necrotizing granulomas comprised of epithelioid histiocytes with or without giant cells characterize this entity, typically with multi-organ involvement. While the granulomas of sarcoidosis are usually morphologically distinguishable from the poorly formed granulomas of PBC, the granulomas of PBC are typically a component of bile duct destruction, whereas granulomas of sarcoidosis generally appear as a “bystander” inflammatory process, providing an architectural aid in discerning these entities [13-16].

References:

1. Deltenre P, Valla DC. Ischemic cholangiopathy. J Hepatol. 2006 Apr;44(4):806-17.
2. Viola S, Meyer M, Fabre M, et al. Ischemic necrosis of bile ducts complicating Schonlein-Henoch purpura. Gastroenterology 1999;117:211-214.
3. Jennette JC, Falk RJ, Bacon PA, et al. 2012 Revised International Chapel Hill Consensus Conference Nomenclature of Vasculitides. Arthritis Rheum. 2013 Jan;65(1):1-11.
4. Barquist ES, Glodstein N, Zinner MJ. Polyarteritis nodosa presenting as a biliary stricture. Surgery 1991;109:16-19.
5. Tinazzi I, Caramaschi P, Parisi A, et al. Pancreatic granulomatous necrotizing vasculitis: a case report and review of the literature. Rheumatol Int. 2007 Aug;27(10):989-91.
6. Trabelsi ABS, Issaoui D, Ksiaa M, et al. Sclerosing cholangitis in Behçet’s disease. Case Rep Med. 2013;2013:692980.
7. Hernández-Rodríguez J, Tan CD, Rodríguez ER, et al. Single-organ gallbladder vasculitis: Characterization and distinction from systemic vasculitis involving the gallbladder. An analysis of 61 patients. Medicine (Baltimore). 2014 Nov; 93(24):405-413.
8. Zhang X, Furth EE, Tondon R. Vasculitis involving the gastrointestinal system is often incidental but critically important. Am J Clin Pathol. 2020 Sep 8;154(4):536-552.
9. Deshpande V, Sainani NI, Chung RT, et al. IgG4-associated cholangitis: a comparative histological and immunophenotypic study with primary sclerosing cholangitis on liver biopsy material. Mod Pathol. 2009 Oct;22(10):1287-95.
10. Deshpande V, Zen Y, Chan JKC, et al. Consensus statement on the pathology of IgG4-related disease. Mod Pathol 2012.
11. Lindor KD, Bowlus CL, Boyer J, et al. Primary biliary cirrhosis: 2018 practice guidance from the American Association for the Study of Liver Diseases. Hepatology. 2019 Jan;69(1)394-419.
12. Selvan O, Vij M, Narasiman G, et al. Sarcoidosis mimicking primary biliary cirrhosis – a clinic-pathological description. Trop Gastroenterol. Jul-Sep 2015;36(3):207-9.
13. Farooq PD, Potosky DR. The Klatskin tumor that wasn’t: an unusual presentation of sarcoidosis. AGC Case Rep J. 2016 Oct 12;3(4):e141.
14. Gaduputi V, Ippili R, Sakam S, et al. Extrahepatic biliary obstruction: an unusual presentation of hepatic sarcoidosis. Clin Med Insights Gastroenterol. 2015 Apr 19;8:19-22.
15. Jebran AF, Schmidt WE, Kahraman A, et al. Sarcoidosis of the intra- and extrahepatic bile ducts with concomitant cholangitis in a patient with ulcerative colitis. Case Rep Gastroenterol. 2019 Mar 29;13(1):153-158.
16. Lewis J. Histopathology of granulomatous liver disease. Clin Liver Dis (Hoboken). 2018 Apr 6;11(3)77-80.

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Case contributed by:

Christopher M Sande MD

Zhaohai Yang MD PhD

Department of Pathology and Laboratory Medicine
Perelman School of Medicine at the University of Pennsylvania

Conflict of Interest: NO

Answer: Medullary carcinoma

Microscopic appearance:

Histopathological examination revealed a cellular neoplasm composed of relatively monomorphic cells with high N:C ratio and vesicular nuclei. The neoplasm had a syncytial growth pattern without obvious gland formation (Figure 1), scant stroma and overall pushing border (Figure 2) with focal microscopic infiltrative interface with the adjacent tissues (Figure 3). There was also a diffuse lymphocytic infiltration within the tumor (tumor-infiltrating lymphocytes, TILs). No confluent necrosis was identified. Lymphovascular invasion (involving both lymphatic spaces and large vessels) and lymph node metastases (in two lymph nodes, with extranodal extension) were present. No in-situ lesions, such as pancreatic intraepithelial neoplasia (PanIN) or adenomatous change in the duodenal or ampullary mucosa were identified.  

Immunohistochemistry:

Performed immunohistochemical stains reveal that the tumor cells are positive for CK7 (Figure 4), MUC1/ EMA (Figure 5), and CK8/18, while negative for CK20, CDX2, MUC2, MUC5AC, Chromogranin, and Synaptophysin. CD3 highlighted intra- and peri-tumoral T lymphocytes, CD20 highlighted some peri-tumoral B lymphocytes, no intratumoral B lymphocytes were identified. Althoug expression of MLH1 and PMS2 proteins was retained, expression of MSH2 (Figure 6) and MSH6 proteins was absent in the cells. EBV-encoded RNA (EBER) in-situ hybridization was also negative in the tumor cells.

Molecular analysis:

Multiplex PCR for MSI, using HNPCC KIT 1-FL with 5 MSI markers (BAT-25, BAT-26, NR-21, NR-22, NR-24) reveled alterations in all 5 molecular markers, indicating microsatellite instable phenotype (MSI-H).

Final histological diagnosis: Medullary carcinoma of the pancreas.

Discussion:

Medullary carcinoma of the pancreas is a rare subtype of pancreatic neoplasms, pathogenetically and behaviorally distinct from pancreatic ductal adenocarcinoma (PDAC)¹. Recognition of this subtype is important, not only for prognostic, but also for therapeutic purposes. Syncytial growth pattern composed of pleomorphic cells with no gland formation, pushing borders and the presence of intra- and peri-tumoral lymphocytes are helpful histological findings.

Medullary carcinoma of the pancreas has been recognized as a distinct but rare entity for only about two decades (first reported in 1998 by Goggins M et al²). Unlike conventional PDAC, the incidence of KRAS mutations is very low in this tumor type. Medullary carcinoma of the pancreas has a better prognosis than conventional PDAC³. Like other medullary carcinomas involving the tubular gastrointestinal tract, a significant proportion of medullary carcinomas of the pancreas reveal high microsatellite instability (MSI)⁴. A subset of these patients has been shown to carry germline mutations of mismatch repair genes (Lynch syndrome). Isolated cases with synchronous/metachronous colonic adenocarcinoma linked to Lynch syndrome have been reported⁵. In cases that are not linked to Lynch syndrome, there is an increased association with family history of other cancers. A case of medullary carcinoma of the pancreas was reported to be associated with EBV⁵.

With the current advances in oncology, promising treatment modalities have emerged, such as using immune checkpoint inhibitors in solid tumors with MSI-high phenotype, including pancreatic cancers⁶. Although MSI-high phenotype is very rare in conventional PDACs, overall accounting for <1% of all cases⁷; given its important therapeutic implications, MSI should at least be routinely investigated in the pancreatic cancer types in which an increased frequency of MSI-high phenotypes are encountered, such as medullary carcinoma or colloid carcinoma, and results should be integrated into the final pathology report.

Medullary carcinomas should be distinguished from

– Poorly differentiated pancreatic ductal adenocarcinomas, which almost always have some degree of gland formation, usually reveal an abundant desmoplastic stroma, an infiltrative growth pattern, and at least a focal intracytoplasmic mucin production.

– Poorly differentiated neuroendocrine carcinomas, which are composed of tumor cells arranged in nests and sheets, usually show an infiltrative growth pattern and abundant intratumoral necrosis. Granular chromatin and nuclear molding would also suggest neuroendocrine differentiation, and staining for neuroendocrine markers (chromogranin and synaptophysin) would confirm the diagnosis. There are also usually no intratumoral lymphocytes, unlike medullary carcinomas.

– High-grade lymphoma, such as diffuse large B-cell lymphoma, would also usually have a syncytial growth pattern, but intratumoral infiltration with mature lymphocytes are not a feature. Specific immunohistochemical stains to ascertain the cell lineage is necessary for the correct diagnosis.

– Metastatic melanoma is a consideration on H&E evaluation. Relevant history and immunohistochemical markers are necessary to exclude this diagnosis.

References:

1. WHO Classification of Tumours Editorial Board. Digestive system tumours. Lyon (France): International Agency for Research on Cancer; 2019.
2. Goggins M, Offerhaus GJ, Hilgers W, Griffin CA, Shekher M, Tang D, Sohn TA, Yeo CJ, Kern SE, Hruban RH. Pancreatic adenocarcinomas with DNA replication errors (RER+) are associated with wild-type K-ras and characteristic histopathology. Poor differentiation, a syncytial growth pattern, and pushing borders suggest RER+. Am J Pathol. 1998 Jun;152(6):1501-7. Am J Pathol. 1998 Jun;152(6):1501-7.
3. Mostafa ME, Erbarut-Seven I, Pehlivanoglu B, Adsay V. Pathologic classification of “pancreatic cancers”: current concepts and challenges. Chin Clin Oncol. 2017 Dec;6(6):59.
4. Yamamoto H, Itoh F, Nakamura H, et al. Genetic and clinical features of human pancreatic ductal adenocarcinomas with widespread microsatellite instability. Cancer Res 2001;61:3139-44.
5. Wilentz RE, Goggins M, Redston M, Marcus VA, Adsay NV, Sohn TA, Kadkol SS, Yeo CJ, Choti M, Zahurak M, Johnson K, Tascilar M, Offerhaus GJ, Hruban RH, Kern SE. Genetic, immunohistochemical, and clinical features of medullary carcinoma of the pancreas: A newly described and characterized entity. Am J Pathol. 2000 May;156(5):1641-51.
6. Le DT, Durham JN, Smith KN, Wang H, Bartlett BR, Aulakh LK, Lu S, Kemberling H, Wilt C, Luber BS, Wong F, Azad NS, Rucki AA, Laheru D, Donehower R, Zaheer A, Fisher GA, Crocenzi TS, Lee JJ, Greten TF, Duffy AG, Ciombor KK, Eyring AD, Lam BH, Joe A, Kang SP, Holdhoff M, Danilova L, Cope L, Meyer C, Zhou S, Goldberg RM, Armstrong DK, Bever KM, Fader AN, Taube J, Housseau F, Spetzler D, Xiao N, Pardoll DM, Papadopoulos N, Kinzler KW, Eshleman JR, Vogelstein B, Anders RA, Diaz LA Jr. Mismatch repair deficiency predicts response of solid tumors to PD-1 blockade. Science. 2017 Jul 28;357(6349):409-413.
7. Luchini C, Bibeau F, Ligtenberg MJL, Singh N, Nottegar A, Bosse T, Miller R, Riaz N, Douillard JY, Andre F, Scarpa A. ESMO recommendations on microsatellite instability testing for immunotherapy in cancer, and its relationship with PD-1/PD-L1 expression and tumour mutational burden: a systematic review-based approach. Ann Oncol. 2019 May 6 [Epub ahead of print].

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Case contributed by:

Claudio Luchini, MD, PhD

Associate Professor of Pathology

Department of Diagnostics and Public Health

Section of Pathology

University and Hospital Trust of Verona

37134 Verona, Italy

Email: claudio.luchini@univr.it

Deyali Chatterjee, MD

Assistant Professor

Department of Pathology and Immunology

Washington University School of Medicine

425 S Euclid Ave

St. Louis, MO 63110

Email: deyali@wustl.edu