Extrapancreatic solid pseudopapillary tumors: A clinicopathological analysis of two cases.

Solid pseudopapillary tumors (SPTs) are unusual neoplasms that mostly occur in the pancreas, and predominantly affect young women. As a low-grade malignant neoplasm of the exocrine pancreas, they occasionally metastasize, usually to the liver or peritoneum. It has been reported that <1% of SPTs are primary extrapancreatic SPTs. In the present study, we present two rare, but conspicuous extrapancreatic SPTs. Both occurred in young women, and showed good prognoses following surgery. One was a recurrent SPT of the pancreas that metastasized to the ovary, and the other was a distinct primary neoplasm that arose in the retroperitoneal area. The pathological features of the two tumors, including solid and pseudopapillary growth patterns with pale or eosinophilic cytoplasm, were characteristic of SPTs of the pancreas. However, in the case of the metastatic ovarian tumor, focal necrosis and an increased nuclear-to-cytoplasmic ratio were observed. The presence of positive nuclear-cytoplasmic β-catenin, the loss of membranous E-cadherin expression, and a perinuclear punctate CD99 staining pattern on immunohistochemistical analysis, were essential features for diagnosis. The aim of the present study was to compare the morphological and immunohistochemical features of these tumors with those typical of pancreatic SPTs, and to raise awareness that SPTs are able to metastasize to unusual sites, and may also arise as primary tumors outside the pancreas, which may lead to diagnostic dilemmas.