Clinical history: 43-year-old female with a complex mass with calcifications in the body of the pancreas, found incidentally on imaging.
What is the most probable diagnosis?
Solid pseudopapillary tumour (SPT)
Epidemiology and pathogenesis: The mean age of patients with SPT is 30 years. It occurs more frequently in women, with a 1:9 male to female ratio. Symptoms are non-specific, and some cases are discovered incidentally. The cellular origin of SPT is unknown. Some tumours show endocrine differentiation, with positive CD56 staining and occasional positive synaptophysin. However, chromogranin is always negative. Acinar and ductal markers are also negative.
Gross: SPTs are typically well-circumscribed, soft, friable, yellow-brown masses with hemorrhage. They may show cystic degeneration. With marked cystic change, they may resemble a pseudocyst.
Histology: Microscopically, SPTs are composed of solid nests of cells surrounding small blood vessels. Cells further from the vessels undergo degeneration, leaving a cuff of cells around blood vessels to produce a pseudopapillary architecture. There are no true lumen and the stroma may show variable hyalization. The tumour cells may show marked cytoplasmic vacuolization. The cells have moderate eosinophilic cytoplasm which usually contains eosinophilic hyaline globules. The nuclei are relatively uniform and show longitudinal grooves. Although the tumour is grossly well-circumscribed, the borders are commonly infiltrative on microscopy.
Immunohistochemistry: SPT is positive for vimentin, CD10, CD56, a1-antitrypsin. Keratin and synaptophysin may be positive. Negative markers include trypsin, chromogranin and CEA. Other positive markers include PR, nuclear b-catenin and cyclin D1.
Differential diagnosis: SPT must be distinguished from other solid tumours of the pancreas, including acinar cell acrinoma, mixed acinar cell neoplasm, pancreatoblastoma, and pancreatic endocrine neoplasm. Immunohistochemistry is very useful for this purpose. While SPT is much more common in females, the other neoplasms have an equal sex distribution. Adrenal cortical neoplasms (positive for inhibin), which may show a pseudopapillary pattern, is also in the differential diagnosis.
Natural history: Although biologically malignant, death is rarely attributed to the direct effect of the tumour. Metastases to the liver or peritoneum occur in only 10-15% of cases. Patients with metastatic disease may survive for many years. SPT may rarely undergo high-grade malignant transformation.