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: 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/

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Case contributed by:

Oluwaseyi Olayinka, MD, MSc, Danbury Hospital

Ramapriya Vidhun, MD, Danbury Hospital

Conflict of Interest: NO