Cytopathology Case 12

Final Diagnosis & Discussions:

FINAL DIAGNOSIS: Solid-pseudopapillary tumor

 

DISCUSSION
Solid-pseudopapillary tumor (SPPT) is the preferred term for a distinctive type of pancreatic tumor previously known as “papillary and solid epithelial neoplasm”, “papillary-cystic neoplasm”, and “cystic-solid papillary carcinoma”. [1] The majority of cases occur in young to middle-aged women (mean age is 30 years) and are discovered either incidentally or during evaluation for abdominal discomfort. Grossly, the tumor is often a well-encapsulated, single mass although a solid- infiltrative border is not uncommon. The combination of solid areas intermixed with more cystic/hemorrhagic regions is typical. Histologically, the features are quite characteristic. Most evident is the proliferation of loosely cohesive epithelioid cells that in areas cluster to form multiple layers over thickened/hyalinized blood vessels that form the center of the pseudopapillary structures. The epithelioid cells are generally monotonous and somewhat bland in appearance with occasional nuclear grooves. Additional microscopic findings that are commonly found include hyaline globules, calcifications, and foam cells.

To a large extent, the cytologic characteristics reflect those on histology. The aspirate smears are highly cellular and are composed predominantly of the monotonous epithelioid cell proliferation. The neoplastic cells are loosely cohesive, as evidenced by their arrangement both in loose clusters and as single cells. The most characteristic feature, however, is the presence of blood vessels surrounded by the cellular proliferation. These vessels show thickening with a myxoid or hyalinized substance present around the vessel wall. Under high power inspection the neoplastic epithelioid cells demonstrate oval-shaped nuclei with occasional grooves, inconspicuous nucleoli, and finely granular chromatin. As in histology; hyaline globules, calcifications, and foam cells may be identified. The major differential diagnoses to consider for SPPT are acinar cell carcinoma and pancreatic endocrine neoplasms.

Immunohistochemically, SPPTs are typically negative or focally positive for cytokeratins (Cam 5.2 and AE1/3). In addition, markers for acinar cell differentiation, including trypsin and chymotrysin are also usually negative or only focally positive. Neuroendocrine markers such as CD56, NSE, and synaptophysin may show partial reactivity with SPPTs; however, the most specific marker of neuroendocrine differentiation chromogranin is negative. Of the markers that are positive in SPPTs, combined nuclear and cytoplasmic expression of β-catenin is probably the most useful as this expression is not observed in either acinar cell carcinoma or pancreatic endocrine tumors. Additionally, CD10 and PR are also strongly positive in SPPTs, although these markers should be used more cautiously as both can be positive in pancreatic endocrine tumors as well. [3]

Genetically, SPPTs are distinct from pancreatic ductal adenocarcinomas and almost always exhibit mutations in the β-catenin pathway. In fact, greater than 90% of SPPTs harbor mutations in exon 3 of the β-catenin gene (CTNNB1). The remaining 10% likely have their mutation in other exons of the same gene. Thus, 100% of SPPTs show abnormal cytoplasmic/nuclear pattern of reactivity with β-catenin. This suggests a β-catenin gene mutation that activates the Wnt-signaling pathway is the underlying molecular abnormality in SPPTs.[3] The overall prognosis of SPPTs is excellent with low risk of local recurrence or liver metastases. Therefore, SPPT should be considered as a neoplasm with low malignant potential.[1]

References

  1. Juan Rosai. Rosai and Ackerman’s Surgical Pathology. 9th Edition. Elsevier. 2004. Pages 1082-83.

  2. Edmund S. Cibas and Barbara S. Ducatman. Cytology Diagnostic Principles and Clinical Correlates. Third Edition. Saunders Elsevier. 2009. Page 394.

  3. David J. Dabbs. Diagnostic Immunohistochemistry. Third Edition. Saunders Elsevier. 2010. Pages 555-556.