A solid pseudopapillary tumor arising from the greater omentum followed by multiple metastases with increasing malignant potential.

Solid pseudopapillary tumor is a rare, indolent neoplasm almost exclusively seen in the pancreas. We describe an unusual case of solid pseudopapillary tumor arising in the greater omentum of a 45-year-old man with subsequent multiple liver metastases and peritoneal dissemination. The patient underwent a total of ten laparotomies and died of unresectable disease 8 years after the initial presentation. Microscopically, the primary tumor and the relapsed tumors consistently exhibited identical growth patterns, which were characterized by solid sheets intermingling with pseudopapillary arrangements of uniformly small cells. Immunohistochemical staining was diffusely positive for vimentin and focally positive for alpha-1-antitrypsin. These features were compatible with those of conventional pancreatic solid pseudopapillary tumors. We also performed quantitative evaluation of Ki-67 immunoreactivity and mitotic figures, which indicated malignant transformation of this extremely rare tumor. This is the first detailed report of solid pseudopapillary tumor arising outside the pancreas complicated by repetitive liver metastases and peritoneal carcinomatosis, suggesting the existence of a more lethal subgroup of tumors.