Answer: Serous cystadenoma of the pancreas.

Final diagnosis:  

Serous cystadenoma of the pancreas

Discussion

Serous cystadenomas (SCAs) are benign epithelial neoplasms which account for 1-2% of all pancreatic tumors. They are usually solitary and most frequently involve the pancreatic body or tail. There is a female predominance (3:1) and they are usually discovered incidentally by imaging performed for other reasons. SCAs may be associated with Von Hippel-Lindau syndrome. VHL- associated SCAs develop multiple microcystic and macrocystic serous cystadenomas which are indistinguishable from sporadic SCAs. Sporadic SCAs often carry somatic VHL gene alterations.  Serous cystadenocarcinoma based on the presence of metastasis to other organ(s) has been reported, but it is extremely rare.  The cysts can involve the entire pancreas if associated with germline alteration in VHL gene.  The classic radiologic finding is a well-circumscribed, multilocular microcystic lesion with central scar, sometimes with a “sunburst” calcification pattern due to calcifications involving the thin septa. On EUS, it appears as an echogenic mass with numerous cysts producing a characteristic honeycomb appearance. Histologically, the cysts are lined by a single layer of cuboidal to flat epithelial cells with clear cytoplasm, well defined cell border, and small round nuclei with inconspicuous nucleoli, and without any pleomorphism or atypia. Underlying the epithelium is an interweaving network of capillaries. The central scar consists of hyalinized stroma with fewer clusters of tiny cysts.   Due to presence of glycogen, the clear cells are positive for cytoplasmic granules on PAS which are sensitive to diastase. SCA may bleed spontaneously or after FNA/biopsy, which may lead to extensive scar and degenerative changes with only minimal remaining cystic epithelium.

As previous studies have demonstrated, the diagnosis of SCA can be very challenging on cytology and small biopsy. Cytology/biopsy specimens are usually paucicellular. Without knowledge of the characteristic imaging findings and chemical analysis of the cyst fluid, serous cystadenomas are not always recognized preoperatively. Scant cellular yield on fine-needle aspiration or biopsy often leads to a nondiagnostic or nonspecific benign diagnosis unless attention is paid to the subtle findings (1-2). The hint for diagnosis on low power lies in the hyalinized stroma which on high power can show embedded small cysts lined by flattened /clear cuboidal cells, sometimes mimicking vascular proliferation, especially since these cysts are also associated with a prominent capillary network. At other times, failure to recognize the cyst lining can be interpreted as non-diagnostic stroma of a pseudocyst. Judicious use of PAS histochemical stain with or without digestion, along with, immunohistochemical stains such as CK7 and inhibin can help in confirming the diagnosis. (Caveat: reportedly, α-inhibin sensitivity by immunohistochemistry was observed to be 80% in resected cases, but only 59% in cell block/biopsy specimens (3). GLUT-1 immunostaining may also be useful to highlight the epithelium of SCA. However, PanINs/IPMNs and ductal adenocarcinoma can also show variable expression, based on grade of lesion (4), and staining must be taken in context. Cyst fluid analysis of SCAs typically shows low CEA levels (typically <5 ng/mL) and amylase levels (typically <250 U/L). Presence VHL mutation on molecular analysis of cystic fluid also help to confirm the diagnosis of SCA.

Differential diagnosis:

Acinar Cystic Transformation of the Pancreas:

Acinar cystic transformation of the pancreas is a rare cystic lesion arising from dilatation of an acinar-ductal unit, with fewer than 100 cases have been described in literature (5). Currently, WHO classifies acinar cystic transformation as a non-neoplastic cystic lesion (6).  Cases are divided into two categories: clinically recognized macroscopic multilocular lesions and incidental unilocular microscopic findings. They have female predominance of 3:1 and have been associated with random X-chromosome inactivation (7). The multilocular cyst can diffusely involve the pancreas and rarely communicate with the main pancreatic duct. Histologically they consist of variably sized cysts with incomplete septa, surrounded by pancreatic parenchyma. Unilocular lesions have underlying thin or thick hyalinized walls. The cysts are lined by pale ductal epithelium with interspersed acinar cells with granular apical cytoplasm and basally oriented nuclei. No nuclear atypia or mitotic activity has been reported. Immunohistochemically, these cysts are diffusely positive for CK7 with patchy staining for CK19 in ductal cells; and trypsin, chymotrypsin, and BCL10 staining the acinar component. Acinar cystic transformation is regarded as a benign process, and there has been no reports of malignant transformation (8).  Acinar cystic transformation lacks the glycogen rich epithelium of serous cystadenomas. These lesions may be difficult to differentiate on small biopsy.

Hemangioma:

Pancreatic hemangiomas are extremely rare, especially in adults, and is considered a benign vascular tumor. To date, about 20 cases have been reported in the English literature (9). In difficult cases, vascular markers (CD34, CD31, ERG) and CK7 can be used to distinguish vascular spaces from small cysts of SCA.

Clear cell renal cell carcinoma (ccRCC):

Secondary neoplasms affecting the pancreas are uncommon, accounting from 2% to 5% of all malignancies in the pancreas. The most common metastases to the pancreas include renal cell carcinoma, melanomas, colorectal carcinomas, lung carcinomas, breast carcinomas, and sarcomas. ccRCC should always be considered when encountering pancreatic lesions with “clear” cytoplasm. Approximately 55% of patients with metastatic renal cell carcinoma to pancreas are asymptomatic, and the disease may manifest after a mean time intervals of > 10 years during which the patient may be disease free. Cytologic atypia, positivity for PAX-8 and CD10, along with the patient remote history of RCC, are helpful clues that can distinguish renal cell carcinoma from solid form of serous cystadenoma (10).

Well differentiated clear cell neuroendocrine tumor of the pancreas:

Well differentiated clear cell neuroendocrine tumors of the pancreas may be sporadic or associated with VHL syndrome or multiple endocrine neoplasia type I. The solid area of SCAs shares similar morphologic features of a well differentiated clear cell neuroendocrine tumors. Positive staining for neuroendocrine markers: chromogranin, synaptophysin and INSM1 would confirm the diagnosis of a well differentiated clear cell neuroendocrine tumor.

References:

1. Huang P, Staerkel G, Sneige N, Gong Y. Fine-needle aspiration of pancreatic serous cystadenoma: cytologic features and diagnostic pitfalls. Cancer. 2006 Aug 25;108(4):239-49. doi: 10.1002/cncr.21911. PMID: 16691573.
2. Salomao M, Remotti H, Allendorf JD, Poneros JM, Sethi A, Gonda TA, Saqi A. Fine-needle aspirations of pancreatic serous cystadenomas: improving diagnostic yield with cell blocks and α-inhibin immunohistochemistry. Cancer Cytopathol. 2014 Jan;122(1):33-9. doi: 10.1002/cncy.21347. Epub 2013 Aug 12. PMID: 23939868.
3. Steel M, Rao S, Ho J, et al. Cytohistological diagnosis of pancreatic serous cystadenoma: a multimodal approach. J Clin Pathol 2019; 72:615–621.
4. Basturk O, Singh R, Kaygusuz E, Balci S, Dursun N, Culhaci N, Adsay NV. GLUT-1 expression in pancreatic neoplasia: implications in pathogenesis, diagnosis, and prognosis. Pancreas. 2011 Mar;40(2):187-92. doi: 10.1097/MPA.0b013e318201c935. PMID: 21206329; PMCID: PMC3164314.
5. Rift CV, Hasselby JP, Hansen CP, Federspiel B. Acinar cystic transformation of the pancreas: report of a case and a review of the literature. Pathol Res Pract. 2020;216(6):152928)
6. WHO classification of tumors series, 5th ed.; vol. 1). http://publications.iarc.fr/579.2019
7. SongM.-Z., SuC.-H., & HsiaoC.-H. (2015). Acinar Cell Cystadenoma of Retroperitoneum: A Case Report and the Literature Review. JOP. Journal of the Pancreas, 16(3), 307-309. https://doi.org/10.6092/1590-8577/3002
8. Luchini C, et al. Acinar Cystic Transformation of the Pancreas: Histomorphology and Molecular Analysis to Unravel its Heterogeneous Nature. Am J Surg Pathol. 2023 Mar 1;47(3):379-386. Epub 2023 Jan 16. PMID: 36649476
9. Jin C, Mo JG, Jiang H, Wang LZ, Zou H, Wang KP. Adult pancreatic hemangioma: a rare case report and literature review. BMC Surg. 2020 Jun 3;20(1):118. doi: 10.1186/s12893-020-00779-8. PMID: 32493358; PMCID: PMC7268514.
10. Cheng SK, Chuah KL. Metastatic Renal Cell Carcinoma to the Pancreas: A Review. Arch Pathol Lab Med. 2016 Jun;140(6):598-602. doi: 10.5858/arpa.2015-0135-RS. PMID: 27232353.

Case contributed by:

Sara Alexandria Sherman, MD – PGY-1, Baylor College of Medicine, Houston TX
Shilpa Jain, MD – Associate Professor, Gastronintestinal and Liver Pathology, Baylor College of Medicine, Houston TX

Acknowledgment:

Special thanks to Deyali Chatterjee, MD at MD Anderson Cancer Center for her consultative expertise.

Conflict of Interest: No

Answer: Intracholecystic Tubular Non-mucinous Neoplasm (ICTN) with high-grade dysplasia.

Final diagnosis:  

Intracholecystic Tubular Non-mucinous Neoplasm (ICTN) with high-grade dysplasia.

Discussion

Intracholecystic Tubular Non-mucinous Neoplasm (ICTN) is an unusual type of intracholecystic neoplasm of the gallbladder, recently described as having distinct histologic findings from those of ICPN [1]. Pehlivanoglu et al. [1] analyzed 28 cases of ICTN. Demographic data revealed female/male ratio of 0.9, mean age of 51 years, and mean tumor size of 1.6 cm. The tumors presented as mass-forming lesions comprised of tightly packed, back-to-back, small tubule/glands with areas of cribriform architecture. The tubules/glands were lined by cuboidal, non-mucinous epithelium with high nuclear:cytoplasmic ratio and eosinophilic cytoplasm.

Nuclei were overlapping, round or ovoid with occasional nucleoli and clearing of the chromatin, reminiscent of the nuclear features seen in papillary thyroid carcinoma (Figure 3). The levels of nuclear atypia and architectural changes qualified as high-grade dysplasia in all cases. Squamoid morules were frequently noted. Amorphous amyloid-like hyalinization was sometimes present in the stroma. Immunohistochemical findings [1] showed diffuse positivity of MUC6 (about 70% of cases), scattered positivity of CDX2 (50%), particularly within squamoid morules and labeling for MUC5AC (10%). β-catenin showed diffuse nuclear expression in the tumor cells as well as the morular cells in two (2) cases.

The background gallbladders were without chronic inflammation/injury. Cholesterolosis/cholesterol polyps were commonly seen. However, there was no dysplasia in the background gallbladders and no association with invasive carcinoma. The authors also reviewed >600 gallbladder carcinomas in association with the initial characterization of ICTN and found no residual or associated lesions with similar features to the described cases of ICTN.

The pathogenesis of ICTN has not been fully elucidated but may be associated with alteration of Wnt/β-catenin pathway. Lesions with similar morphology have previously been considered as either a pyloric type of ICPN or as a type of PGA [3].  In summary, cases similar to the one presented here appear to have distinct features from ICPN, occurring in gallbladders with largely normal mucosa and without an associated invasive carcinoma. Further investigation with additional cases is needed to follow to fully establish these features, relationships to other biliary neoplasms and clinical behavior.

Differential diagnosis:

ICPN is a precancerous lesion of the gallbladder. Grossly it forms a distinct polypoid/exophytic intraluminal mass and microscopically shows papillary and/or tubular configuration with dysplasia, which can have four major morphological patterns, e.g., biliary, intestinal, gastric, oncocytic, or combination of these morphologically patterns [2, 4]. Regarding the molecular characteristics of ICPN, mutations in STK11 and CTNNB1 have been identified [3]. Surrounding mucosal epithelium may be associated with dysplasia as well.  About 50% of ICPNs are associated with invasive adenocarcinoma, but it has a better clinical outcome compared to conventional gallbladder adenocarcinomas.

PGA of the gallbladder is a polypoid neoplasm consisting of uniform, back-to-back mucinous glands with pyloric or Brunner gland features.  Positive β-catenin by IHC and mutation of CTNNB1 were identified in 60% of PGAs [2]. They also show diffuse and strong positivity of MUC6. 20% of PGAs contain squamoid morules. PGAs may also have variation in the amount of cytoplasmic mucin, with mucin-poor variants identified, although this is not the typical morphology [3]. Similar to ICTN, multifocality (field effect) is not a feature of PGAs [2]. Taken together, ICTNs are considered to have overlapping pathologic features with PGAs, but the recent characterization of ICTN suggests that they should be considered separate entity from mucinous PGAs [3].

BilIN is a microscopic, non-invasive, flat or (micro)papillary neoplastic lesion, usually not grossly visible.  KRAS mutations were identified in about 40% of cases as an early molecular event of carcinogenesis. It is often present in the mucosa adjacent to the carcinomas. BilIN is graded as low-grade and high-grade according to the degree of cytologic atypia and architectural changes. Low grade is of no clinical significance but high grade warrants extensive sampling to detect an occult invasive carcinoma [2].

References:

1. Pehlivanoglu B, Balci S, Basturk O, Bagci P, Erbarut Seven I, Memis B, Dursun N, Jang KT, Saka B, Ohike N, Tajiri T, Roa JC, Sarmiento JM, Reid MD, Adsay V. Intracholecystic tubular non-mucinous neoplasm (ICTN) of the gallbladder: a clinicopathologically distinct, invasion-resistant entity. Virchows Arch. 2021 Mar;478(3):435-447. 
2. Basturk O, Aishima S, Esoposito I. World Health Organization Classification of Tumours. Intracholecystic papillary neoplasm. In: Digestive System Tumours. 2019, IARC, Lyon.
3. Fukumura Y, Rong L, Maimaitiaili Y, Fujisawa T, Isayama H, Nakahodo J, Kikuyama M, Yao T. Precursor Lesions of Gallbladder Carcinoma: Disease Concept, Pathology, and Genetics. Diagnostics (Basel). 2022 Jan 28;12(2):341.
4. 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. 

Case contributed by:

Goo Lee, MD- University of Alabama at Birmingham.

Acknowledgment:

Special thanks to Volkan Adsay, MD, Koc University Hospitals, Turkey, for his consultative expertise.

Conflict of Interest: No

Answer: Well-differentiated pancreatic neuroendocrine tumor (Pan-NET), lipid rich variant.

Final diagnosis:  

Well-differentiated pancreatic neuroendocrine tumor (Pan-NET), lipid rich variant.

Educational Objectives and Discussion

Educational Objectives

1. Identify and describe the histologic features of lipid rich variant of PanNET
2. Review the clinical implications of a diagnosis of lipid rich variant of PanNET
3. Discuss the differential diagnosis for lipid rich variant of PanNET

Discussion
Immunohistochemical stains were performed on the biopsy material. The neoplastic cells were positive for pan-CK (strong and diffuse), synaptophysin (strong and diffuse) [Figure 2], chromogranin (strong but focal) and inhibin (strong and diffuse) while negative for CK7, RCC, PAX-8, S-100, Melan-A (MART-1), and beta catenin. A MIB-1 (Ki-67) stain showed a low proliferation index (<3%). A diagnosis of well-differentiated pancreatic neuroendocrine tumor, Grade 1, lipid rich variant was rendered.

The patient subsequently underwent surgical resection (pancreaticoduodenectomy). Sectioning of the pancreas revealed a tan-white to tan-yellow, stellate, firm, fibrous mass measuring 4.0 cm in greatest dimension. The microscopic and immunophenotypic features of the tumor in the resection specimen mirrored those of the biopsy material. Sections showed neoplastic cells arranged in nests/clusters and cords, surrounded by marked collagenized/fibrotic stroma [Figure 3]. The tumor cells demonstrated clear/foamy vacuolated cytoplasm and small uniform nuclei with finely dispersed chromatin [Figure 4]. Mitotic figures were virtually absent. The MIB-1 (Ki-67) stain was repeated on the resection specimen and showed a proliferation index of 5-7% in hot spots. A final diagnosis of well-differentiated pancreatic neuroendocrine tumor, Grade 2, lipid rich variant was rendered

PanNET with vacuolated, lipid rich cytoplasm was first described in 1997 by Ordonez and Silva [1]. Singh et al and Xue et al’s series on PaNET variant cases both offered additional valuable contributions to the literature [2,3]. The lipid rich variant affects both men and women and can occur in the head or tail of the pancreas, ranging in size from 2-11 cm. Microscopically, this variant represents a diagnostic challenge (see differential diagnosis section). The prototypical neuroendocrine growth pattern may be absent. The cytologic features are deceptively bland; tumor cells are characterized by round to pyknotic nuclei with fine chromatin and inconspicuous nucleoli. The classic stippled “salt and pepper” chromatin may not be evident. Nuclear “endocrine” atypia is also not identified. The cytoplasm is not only clear but also finely vacuolated; lipid droplets and neuroendocrine secretory granules can be identified ultrastructurally with electron microscopy. Mitotic activity is absent to low and MIB-1 (Ki-67) staining usually does not exceed 5% based on published data [2,3]. Given how unusual these histologic features are compared to a typical low grade neuroendocrine tumor, immunohistochemical stains are an essential adjunct aid. The neoplastic cells routinely express pan-cytokeratin and neuroendocrine markers chromogranin and synaptophysin (focal to diffuse staining). Inhibin and HIF-1α staining can be seen in a subset of tumors, while Melan-A (MART-1) and MUC6 expression is absent [2].
Xue et al. include the lipid rich variant in the “aggressive variant group” alongside hepatoid, oncocytic, plasmacytoid, and discohesive variants due to propensity for greater tumor size, T-stage, metastases, and progression rates [3]. Furthermore, patients with lipid rich PanNET fall into one of two categories: younger patients with familial/functional/syndromic tumors (rare) and older patients with non-functioning/sporadic tumors (common). While inhibin, HIF-1α, and Melan-A (MART-1) expression by immunohistochemistry in clear cell PanNET has a strong association with von Hippel Lindau (VHL) disease, this correlation is less robust in lipid rich PaNET [2,4]. Regardless, it may still be prudent for clinicians to exclude VHL disease or MEN1 (multiple endocrine neoplasia type 1) syndrome as lipid rich PaNETs have rarely been reported in these patients [2].

Differential diagnosis:

The pathologist should keep a broad differential diagnosis in mind when approaching a low-grade pancreatic lesion with clear/vacuolated cytoplasm:
Clear cell PanNET:
PanNET with clear cell change are not uncommon and have a strong association with VHL disease, particularly when HIF-1α, inhibin, and/or Melan-A (MART-1) expression by immunohistochemistry is seen in addition to traditional neuroendocrine markers. VHL-associated clear cell PanNETs usually occur in younger women and are non-functioning tumors [4-7]. While the cytoplasm is clear, it lacks the vacuolated/microvesicular appearance of lipid rich PanNET.
Solid pseudopapillary neoplasm (SPN):
SPNs are uniquely characterized by pseudopapilla, nuclear grooves, and hyaline globules. SPNs can exhibit clear cytoplasm and frequently contain foamy macrophages, and therefore could appear similar to lipid rich PanNET in small biopsy specimens. While SPNs can express synaptophysin, chromogranin is usually negative. More importantly, nuclear staining of the neoplastic cells with beta catenin is a key diagnostic clue for the diagnosis of SPN, reflecting underlying mutations in CTNNB1 [8]. Additionally, these tumors most commonly occur in adolescent girls/young women under the age of 35 and arise most frequently in the body or tail of the pancreas.
Perivascular epithelioid cell tumor (PEComa or so called “sugar tumor”):
PEComas are rare mesenchymal neoplasms with myomelanocytic differentiation. The tumors grow in sheets or nests and are characterized by epithelioid cells with clear to eosinophilic, granular cytoplasm, which has a moth-eaten appearance (“spider cells”) with a spindle cell component present in a minority of cases. Co-expression of smooth muscle markers (SMA, desmin, h-caldesmon) and melanoma markers (e.g. Melan-A/MART-1, HMB45) is characteristic. Neuroendocrine labeling and strong and diffuse keratin expression is notably absent [8].
Morphologic patterns of pancreatic ductal adenocarcinoma:
While pancreatic ductal carcinoma typically shows significant cytologic atypia and has a uniquely infiltrating gland-forming growth pattern accompanied by a desmoplastic stromal response, certain morphologic patterns can appear deceptively bland and lack gland formation. The foamy gland and clear cell patterns of invasive ductal adenocarcinoma of the pancreas both are included in this category. Helpful distinguishing characteristics from lipid rich PanNET include gland formation, possible presence of mucin and the lack of neuroendocrine marker expression. Additionally, PanNETs most often present as well-circumscribed lesion on imaging/EUS/gross examination, as opposed to the poorly-defined, infiltrative growth pattern seen with ductal adenocarcinomas [8].
Adrenal cortical tissue/neoplasm:
Adrenal cortical tissue/neoplasms share many overlapping histopathologic features with lipid rich PanNET and immunohistochemistry can be a helpful aid. Adrenal cortical lesions mark with antibodies to SF-1, calretinin, inhibin, Melan-A (MART-1), and CD68 [9]. Adrenal cortical lesions however lack keratin and neuroendocrine marker positivity. Please note, that inhibin expression (as in our case) can be seen in a subset of lipid rich PanNET; therefore, a broad panel of stains is essential.
Clear cell renal cell carcinoma (ccRCC):
ccRCC should always be considered when encountering pancreatic lesions with “clear” cytoplasm. Renal cell carcinoma is in fact the most common reason for a metastasis to the pancreas. While PAX-8 is a helpful ancillary screening marker used for renal cell carcinoma, it is important to note that PanNET can also express PAX-8 [10]. Therefore, additional antibodies such as RCC and CD10 (for renal cell carcinoma) and synaptophysin and chromogranin (for PaNET) should be included as part of the larger panel of stains.

References:

[1] Ordonez NG, Silva EG. “Islet cell tumor with vacuolated, lipid rich cytoplasm: a new histologic variant of islet cell tumor.” Histopathology 1997; 31:157-160.
[2] Singh R, Reid MD et al. “Lipid-rich variant of pancreatic endocrine neoplasms.” Am J Surg Pathol 2006; 30:194-200.
[3] Xue Y. et al “Morphologic variants of pancreatic neuroendocrine tumors: clinicopathologic analysis and prognodtic stratification.” Endocr Pathol 2020 31:3, 239-253.
[4] Hoang MP, Hruban RH et al. “Clear cell endocrine pancreatic tumor mimicking renal cell carcinoma: a distinctive neoplasm of von Hippel Lindau disease.” Am J Surg Pathol 2001; 25:602-609.
[5] Guarda LA, Silva EG et al. “Clear cell islet cell tumor.” Am J Surg Pathol 1983; 79:512-517.
[6] Mount SL, Weaver DL et al. “Von Hippel Lindau disease presenting as a pancreatic neuroendocrine tumor.” Virchows Arch 1995; 426:523-528
[7] Musso C, Paraf F. et al. “Pancreatic neuroendocrine tumors and von Hippel Lindau disease” Ann Pathol. 2000; 20:130-133.
[8] Nagtegaal ID, Odze RD, Klimstra D, Paradis V, Rugge M, Schirmacher P, Washington KM, Carneiro F, Cree IA; WHO Classification of Tumours Editorial Board. The 2019 WHO classification of tumours of the digestive system. Histopathology. 2020 Jan; 76(2):182-188. doi: 10.1111/his.13975. Epub 2019 Nov 13. PMID: 31433515; PMCID: PMC7003895.
[9] Sangoi A., Fujiwara M et al. “Immunohistochemical Distinction of Primary Adrenal Cortical Lesions from Metastatic Clear Cell Renal Cell Carcinoma: A Study of 248 Cases.” Am J Surg Pathol 2011; 35(5): 678-686.
[10] Bellizi AM “Immunohistochemistry in the diagnosis and classification of neuroendocrine neoplasms: wat can brown do for you?” Hum Pathol 2020; 96:8-33.

Case contributed by:

Susanne K. Jeffus, MD – University of Arkansas for Medical Sciences
Camila Simoes, MD – University of Arkansas for Medical Sciences
Felicia D. Allard, MD – University of Arkansas for Medical Sciences

Acknowledgment:

Special thanks to David Klimstra, MD, of Memorial Sloan Kettering Cancer Center for his consultative expertise.

Conflict of Interest: No

Answer: Metastatic solid-pseudopapillary neoplasm  of the pancreas

Final diagnosis:  

Metastatic solid-pseudopapillary neoplasm  of the pancreas after a 25 year interval

Discussion

This patient’s case is a rare example of metastatic solid pseudopapillary neoplasm of the pancreas to the liver after a long interval. While the presence of a primary solid-pseudopapillary neoplasm of the pancreas was not able to be definitively verified histologically in this case, multiple features of the patient’s history point to a potential misdiagnosis of her original tumor. The description of a “centrally necrotic” islet cell tumor is unusual. While necrosis can certainly be seen in well-differentiated neuroendocrine tumors, it is more commonly seem in higher grade tumors, which in turn, would be unlikely to show such indolent behavior over 25 years. The reported size of her original tumor, over 8 cm, is also somewhat unusual in terms of risk of progression over such a long time interval. Mostly likely, the original tumor represented a solid pseudopapillary neoplasm of the pancreas where large tumor size and necrosis are very common and the vast majority of tumors demonstrate very indolent behavior, as will be discussed in more detail below.

Solid-pseudopapillary neoplasms (SPN) of the pancreas are rare neoplasms, representing 1-2% of all pancreatic tumors. They are most commonly seen in younger women (90% female predominance) with a mean age at diagnosis of 29 years. For reference, our patient would have been 30 at the time of her original pancreatic surgery. Radiologically they are circumscribed to encapsulated heterogenous lesions, often with cystic degeneration. Grossly, SPN recapitulate this radiographic appearance and are variably mixed solid and cystic tumors with abundant necrosis/degenerative changes and hemorrhage (Figure 9, representative image). SPN can be located anywhere in the pancreas, but are most typically seen in the body/tail.

Histologically, tumors are comprised of loosely cohesive cells surrounding a delicate network of blood vessels, often with associated myxoid stromal change. Pseudopapillae form as the discohesive tumor cells fall apart around the blood vessels, creating the appearance of fibrovascular cores. Intracytoplasmic eosinophilic hyaline globules as well as cytoplasmic clearing and/or intracytoplasmic vacuoles can be seen. Degenerative changes with foamy macrophages, cholesterol clefts, hemorrhage and necrosis are very common in SPN. “Insidious invasion,” where the tumor extends into adjacent pancreas without generating significant stromal reaction is also common, despite an overall circumscribed appearance. Cytologically, the tumor cells of SPN are polygonal with eosinophilic cytoplasm and round to oval nuclei with nuclear grooves. Mitotic figures are rare, but degenerative atypia with pleomorphic nuclei and dark, “smudgy” chromatin and multinucleated atypical giant cells can be seen.

While the morphology of SPN is often very distinctive, there are overlapping features with other cellular neoplasms of the pancreas, most notably well-differentiated neuroendocrine tumors and acinar cell carcinomas.Immunohistochemistry can be very useful in sorting out these differentials. SPN are variably cytokeratin positive and characteristically label for CD56, CD10, and CD99 (perineuclear dot-like staining) as well as AR, PR, TFE3 and LEF1. Variable labeling with synaptophysin is typical, which can be misleading, particularly on a small biopsy, however, SPN should be negative for chromogranin, in contrast with well-differentiated neuroendocrine tumors of the pancreas, which are typically positive for chromogranin. Over 90% of SPN have a point mutation in exon 3 of CTNNB1, the gene encoding for beta catenin, leading to aberrant nuclear and cytoplasmic labeling with beta catenin antibodies. Immunohistochemical stains for E-cadherin and p120 catenin will also show the loss of membranous expression of these proteins in SPN.

While all SPN are considered to have low malignant potential, overall, the vast majority of cases are cured with surgical resection. Metastatic behavior is rare and can occur after a fairly long time interval from original diagnosis. Liver is the most common site of metastasis. Definitive evidence of clinical and histologic features predicting aggressive behavior and/or future metastases are lacking, although male sex, vascular invasion and perineural invasion, and the presence of metastasis among others, have been proposed. The degenerative atypia described above can be associated with increased Ki67 labeling but does not seem to track with metastatic behavior. Rare cases of SPN with diffuse growth, marked nuclear atypia with sarcomatoid features and markedly elevated mitotic rates have been described and were associated with highly aggressive clinical behavior.

Differential diagnosis:

The differential diagnosis of SPN primarily includes other cellular neoplasms of the pancreas: well-differentiated neuroendocrine tumors, acinar cell carcinoma and pancreatoblastoma. For the rare occurrence of metastatic SPN to the liver, primary liver tumors would also enter the differential, particularly if there was no known history of SPN or a previous pancreas resection.

Of the cellular neoplasms of the pancreas, the majority of morphologic and immunohistochemical overlap with SPN is seen with well-differentiated neuroendocrine tumors. More solid SPN with less cystic degeneration are also more likely to mimic neuroendocrine tumors morphologically. Neuroendocrine tumors can also form some pseudopapillae. Cytologically, the features of these two tumors is fairly distinct with neuroendocrine tumors having finely stippled “salt and pepper” chromatin and eosinophilic to amphophilic cytoplasm. As mentioned above, a major diagnostic pitfall is the combination of keratin, CD56, and synaptophysin reactivity in SPN. Despite these overlaps, SPN are almost uniformly chromogranin negative and neuroendocrine tumors should not show abnormal nuclear staining for beta-catenin. As long as one thinks of the diagnosis of SPN, Immunohistochemical studies can usually distinguish the two entities easily.

Cellular neoplasms with acinar differentiation including acinar cell carcinoma and pancreatoblastoma can be separated from SPN via distinct morphologic, cytologic and Immunohistochemical features. Acinar cell carcinomas have characteristically granular eosinophilic cytoplasm with a single, prominent nucleolus and label with antibodies against exocrine enzymes including trypsin and chymotrypsin. They also show strong granular, cytoplasmic labeling with BCL-10. Acinar cell carcinomas can show aberrant nuclear labeling with beta-catenin due to underlying molecular alterations, however SPN will not show reactivity with exocrine enzymes or BCL-10. Pancreatoblastoma has characteristic squamous morules in addition to acinar and variable neuroendocrine and ductal differentiation. These squamous morules will also show nuclear beta-catenin labeling, however their distinct morphology and areas of acinar differentiation on H&E and by immunohistochemistry will distinguish them from SPN.

While there is less morphologic overlap with primary liver tumors, this differential may arise when SPN metastasize to the liver. Hepatocellular carcinoma can be identified by labeling for Hep-Par1, arginase and glypican3. Intrahepatic cholangiocarcinoma can be identified by gland formation and strong, uniform keratin labeling. Both tumors will also show positivity for in situ hybridization for albumin.

References:

Hruban RH, Pitman MB, Klimstra DS. Tumors of the pancreas. Atlas of tumor pathology. Fourth Series, Fascicle 6 ed. Washington, DC: American Registry of Pathology and Armed Forces Institute of Pathology, 2007.

Abraham SC, Klimstra DS, Wilentz RE, Wu T-T, Cameron JL, Yeo CJ et al. Solid-pseudopapillary tumors of the pancreas are genetically distinct from pancreatic ductal adenocarcinomas and almost always harbor beta-catenin mutations. Am J Pathol. 2002; 160(4):1361-1369.

Klimstra DS, Wenig BM, Heffess CS. Solid-pseudopapillary tumor of the pancreas: a typically cystic carcinoma of low malignant potential. Semin Diagn Pathol. 2000; 17(1):66-80.

Tang LH, Aydin H, Brennan MF, Klimstra DS. Clinically aggressive solid pseudopapillary tumors of the pancreas: a report of two cases with components of undifferentiated carcinoma and a comparative clinicopathologic analysis of 34 conventional cases. Am J Surg Pathol. 2005;29 (4):512-9.

La Rosa S, Bongiovanni M. Pancreatic Solid-pseudpapillary Neoplasm: Key Pathologic and Genetic Features. 2020; 144(7):829-37.

Li L, Othman M, Rashid A, Wang H, Li Z, Katz MH, Lee JE, Pisters PW, Abbruzzese JL, Fleming JB, Wang H. Solid pseudopapillary neoplasm of the pancreas with prominent atypical multinucleated giant tumour cells. Histopathology 2013; 62(3):465-71

Estrella JS, Li L, Rashid A, Wang H, Katz MH, Fleming JB, Abbruzzese JL, Wang H. Solid Pseudopapillary neoplasm of the pancreas: clinicopathologic and survival analyses of 64 cases from a single institution. Am J Surg Pathol 2014; 38(2):147-57.

Case contributed by:

Elizabeth Thompson, MD, PhD, Assistant Professor of Pathology and Oncology

Main submitter’s email: ethomp36@jhmi.edu

Main submitter’s institution: The Johns Hopkins University School of Medicine

Second submitter’s name and title:

Huili Li, MD, Surgical Pathology Assistant

Second submitter’s institution: The Johns Hopkins University School of Medicine

Conflict of Interest: No

Answer: Paraganglioma

Final diagnosis:  

Paraganglioma

Educational Objectives and Discussion:

Educational Objectives

1. Identify and describe a rare case of peripancreatic paraganglioma, a rare neoplastic disease that presents considerable diagnostic difficulty.
2. Review the clinicopathological characteristics of peripancreatic paragangliomas.
3. Discuss differential diagnosis of peripancreatic paragangliomas.

Discussion

Peripancreatic paragangliomas can be diagnostically challenging on small biopsies due to morphologic overlap with other primary pancreatic tumors (1, 2). In this case, an initial diagnosis of atypical epithelioid and spindle cell neoplasm was made on the biopsy and decision was made to proceed with surgery. Grossly, the resection specimen showed a 11.8 cm purple-red, ovoid, well-circumscribed peripancreatic mass surrounded by a thin fibrous capsule. Cut surface displayed a tan-pink to dark red, variegated focally nodular cut surface with multiple dilated vessels and focal areas of hemorrhage (Figure 4). Microscopic examination of the resection specimen showed neoplastic cells arranged in nests and trabeculae within a prominent vascular network (Figure 5-7). The cells were predominantly round to oval with some spindling and moderate to abundant eosinophilic granular cytoplasm. Additional IHC on the resection specimen showed that the tumor cells labeled with synaptophysin (strong), chromogranin (patchy) and S100 (patchy) and were negative for cytokeratin (Figures 8-10). In areas the S100 labeled in a sustentacular pattern (Figure 10). Succinate dehydrogenase (SDH) A and B were intact. A final diagnosis of paraganglioma was made. Subsequent blood work showed elevated plasma and urine catecholamines and molecular testing showed no targetable mutations. While the tumor was initially described radiographically as being located in the pancreatic head, subsequent imaging demonstrated a peri-pancreatic localization, much more typical of this entity. It can be critical to consider paraganglioma from both the radiographic and pathologic standpoint as repeated needle biopsies may trigger catecholamine surges and care must be taken during surgical interventions.

The classic microscopic features of paragangliomas are similar irrespective of location and include round-to-polygonal-shaped cells containing amphophilic-to-eosinophilic cytoplasm with stippled, often pleomorphic nuclei containing small inconspicuous nucleoli. In certain cases, cytoplasmic clear cell change, multinucleation, vesicular nuclei, and prominent nucleoli can also be observed (1). The tumor cells usually adopt a nested or organoid (“Zellballen”) pattern separated by highly vascularized fibrous septa. Cases with diffuse growth pattern with only focal areas of nested architecture have been reported (1). In areas of parenchymal invasion, the Zellballen growth pattern can be replaced by irregularly spaced nests of discohesive neoplastic cells. The tumor cells are synaptophysin and chromogranin positive while the surrounding sustentacular cells, label for S100. GATA3 and PHOX2B also show frequent immunoreactivity in extra-adrenal paragangliomas (3-5). Keratin is almost always negative, but rare cases have focal staining. In contrast, paragangliomas in the sacral region are typically keratin positive.

The genetic profile of paraganglioma is similar to that described for pheochromocytomas. Mutations in VHL, RET, NF1, SDHA, SDHB, SDHC, SDHD, SDHAF2, TMEM127, and MAX have been reported (6). Knowledge of these mutations may have significant impact on clinical management and patient outcome. For instance, studies have reported germline mutations in SDHB in up to 30% of patients with metastatic disease arising from sporadic paragangliomas and an association with shorter survival (1, 7, 8). Complete surgical resection of primary and
metastatic disease, when possible provides the highest chance for symptom control. Currently, there are no reliable markers to predict malignancy, except the presence of metastases. Increasing tumor size (>5 cm), increasing Ki-67 proliferation rate, SDHB mutation, and MAX mutation have been reported as risk factors for metastatic behavior (9, 10). Various scoring systems (PASS, GAPP), have been developed to predict risk in pheochromocytomas and paragangliomas (11, 12). Patients with paragangliomas ultimately require follow-up as metastatic disease can appear years after diagnosis.

Differential diagnosis:

The differential diagnosis of peripancreatic paragangliomas includes pancreatic neuroendocrine tumor (PanNET), acinar cell carcinoma (ACC), spindle cell neoplasms, PEComas, and metastatic renal cell carcinoma (RCC).Peripancreatic paragangliomas and PanNET are both neuroendocrine neoplasms thus sharing many of the same characteristics. PanNETs often show distinctive plasmacytoid morphology, usually display round and uniform nuclei and are generally positive for AE1/AE3 and CAM 5.2 while peripancreatic paragangliomas are distinctly negative. Prominent nucleoli typically seen in ACC can be present in peripancreatic paragangliomas. However, the characteristic stippled chromatin of peripancreatic paraganglioma is absent in ACC. The presence of spindle cell morphology/nuclear pleomorphism in peripancreatic paragangliomas can mimic spindle cell neoplasms. These possibilities can usually be distinguished on the basis of immunohistochemistry. Further, the nuclear pleomorphism in paragangliomas typically has a degenerative appearance. Peripancreatic paragangliomas can show cytoplasmic clear cell change thus mimicking metastatic RCCs. However, metastatic RCCs will express PAX8 and are negative for S100 and neuroendocrine
markers.

References:

1. Singhi AD, Hruban RH, Fabre M, Imura J, Schulick R, Wolfgang C, Ali
   SZ. Peripancreatic paraganglioma: a potential diagnostic challenge in
   cytopathology and surgical pathology. Am J Surg Pathol. 2011
   Oct;35(10):1498-504. doi: 10.1097/PAS.0b013e3182281767.
   https://pubmed.ncbi.nlm.nih.gov/21921779/
2. Zeng J, Simsir A, Oweity T, Hajdu C, Cohen S, Shi Y. Peripancreatic paraganglioma mimics pancreatic/gastrointestinal neuroendocrine tumor on fine needle aspiration: Report of two cases and review of the literature. Diagn Cytopathol. 2017 Oct;45(10):947-952. doi: 10.1002/dc.23761. https://pubmed.ncbi.nlm.nih.gov/28560856/
3. Miettinen M, McCue PA, Sarlomo-Rikala M, Rys J, Czapiewski P, Wazny K, Langfort R, Waloszczyk P, Biernat W, Lasota J, Wang Z. GATA3: a multispecific but potentially useful marker in surgical pathology: a systematic analysis of 2500 epithelial and nonepithelial tumors. Am Surg Pathol. 2014 Jan;38(1):13-22. doi: 10.1097/PAS.0b013e3182a0218f. https://pubmed.ncbi.nlm.nih.gov/24145643/
4. Lee JP, Hung YP, O’Dorisio TM, Howe JR, Hornick JL, Bellizzi AM. Examination of PHOX2B in adult neuroendocrine neoplasms reveals relatively frequent expression in phaeochromocytomas and paragangliomas. Histopathology. 2017 Oct;71(4):503-510. doi: 10.1111/his.13243. https://pubmed.ncbi.nlm.nih.gov/28464318/
5. So JS, Epstein JI. GATA3 expression in paragangliomas: a pitfall potentially leading to misdiagnosis of urothelial carcinoma. Mod Pathol. 2013 Oct;26(10):1365-70. doi: 10.1038/modpathol.2013.76. https://pubmed.ncbi.nlm.nih.gov/23599157/
6. Gimenez-Roqueplo AP, Dahia PL, Robledo M. An update on the genetics of paraganglioma, pheochromocytoma, and associated hereditary syndromes. Horm Metab Res. 2012 May;44(5):328-33. doi: 10.1055/s-0031-1301302. https://pubmed.ncbi.nlm.nih.gov/22328163/
7. Brouwers FM, Eisenhofer G, Tao JJ, Kant JA, Adams KT, Linehan WM, Pacak K. High frequency of SDHB germline mutations in patients with malignant catecholamine-producing paragangliomas: implications for genetic testing. J Clin Endocrinol Metab. 2006 Nov;91(11):4505-9. doi: 10.1210/jc.2006-0423. https://pubmed.ncbi.nlm.nih.gov/16912137/
8. Amar L, Baudin E, Burnichon N, Peyrard S, Silvera S, Bertherat J, Bertagna X, Schlumberger M, Jeunemaitre X, Gimenez-Roqueplo AP, Plouin PF. Succinate dehydrogenase B gene mutations predict survival in patients with malignant pheochromocytomas or paragangliomas. J Clin Endocrinol Metab. 2007 Oct;92(10):3822-8. doi: 10.1210/jc.2007-0709. https://pubmed.ncbi.nlm.nih.gov/17652212/
9. Kimura N, Takayanagi R, Takizawa N, Itagaki E, Katabami T, Kakoi N, Rakugi H, Ikeda Y, Tanabe A, Nigawara T, Ito S, Kimura I, Naruse M; Phaeochromocytoma Study Group in Japan. Pathological grading for predicting metastasis in phaeochromocytoma and paraganglioma. Endocr Relat Cancer. 2014 May 6;21(3):405-14. doi: 10.1530/ERC-13-0494. https://pubmed.ncbi.nlm.nih.gov/24521857/
10. Assadipour Y, Sadowski SM, Alimchandani M, Quezado M, Steinberg SM, Nilubol N, Patel D, Prodanov T, Pacak K, Kebebew E. SDHB mutation status and tumor size but not tumor grade are important predictors of clinical outcome in pheochromocytoma and abdominal paraganglioma. Surgery. 2017 Jan;161(1):230-239. doi: 10.1016/j.surg.2016.05.050. https://pubmed.ncbi.nlm.nih.gov/27839933/
11. Kimura N, Takekoshi K, Naruse M. Risk Stratification on Pheochromocytoma and Paraganglioma from Laboratory and Clinical Medicine. J Clin Med. 2018. Sep; 7(9): 242. https://pubmed.ncbi.nlm.nih.gov/30150569/
12. Thompson LD. Pheochromocytoma of the Adrenal gland Scaled Score (PASS) to separate benign from malignant neoplasms: a clinicopathologic and immunophenotypic study of 100 cases. Am J Surg Pathol. 2002 May;26(5):551-66. doi: 10.1097/00000478-200205000-00002. https://pubmed.ncbi.nlm.nih.gov/11979086/

Case contributed by:

Oluwaseyi Olayinka, MD, MSc, Danbury Hospital

Ramapriya Vidhun, MD, Danbury Hospital

Conflict of Interest: NO

 

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