Solid-papillary tumors of the pancreas: histopathology.

A solid-pseudopapillary tumor is an uncommon and "enigmatic" pancreatic neoplasm, and the term encompasses the two most conspicuous histological features: solid and pseudopapillary areas. Grossly, it appears as a large solid, cystic or solid-cystic mass frequently having necrotic and hemorrhagic zones. Histologically, solid-pseudopapillary tumors are generally characterized by solid areas alternating with a pseudopapillary pattern, and cystic spaces which are the results of degenerative changes occurring in the solid neoplasm. Its immunohistochemical pattern is very distinctive and neoplastic cells are consistently vimentin-, CD10- and CD56-positive. Some cases express focal positivity for alpha-1-antitrypsin, alpha-1-antichymotrypsin, neuron-specific enolase and synaptophysin. Progesterone receptors are frequently present. Keratins are not expressed or are found only focally. Endocrine and pancreatic enzyme markers are absent; the origin of solid-pseudopapillary tumors has not yet been clarified. Many investigators favor the theory that solid-pseudopapillary tumors originate from multipotent primordial cells while others suggest an extra-pancreatic origin from genital ridge angle-related cells. Some controversy exists for both hypotheses. Solid-pseudopapillary tumors appear as a low malignancy tumor and only a small number of cases recur or develop metastases after resection. No pathological factors were found to correlate with the prognosis. Some histological features have recently been suggested to be associated with aggressive behavior.