Solid-pseudopapillary tumor of the pancreas: its origin revisited

Solid-pseudopapillary tumor of the pancreas (SPT) has distinctive morpholog ic and biologic features but an unclear origin. It is classified among the pancreatic epithelial tumors, though many are reported to be negative for c ytokeratin. Also unclear are its neuroendocrine differentiation, its capabi lity to express alpha-1-antitrypsin (AAT) and, in view of the tumor's strik ing prevalence in women, its relationship with the female genital tract. To clarify these issues, the immunoprofiles of 59 SPTs were defined by applyi ng a battery of antibodies against cytokeratin, vimentin, neuron-specific e nolase (NSE), synaptophysin, chromogranin A, tyrosine hydroxylase (TH), AAT , LeuM1, Ki-MIP, smooth-muscle actin, CD34, alpha-inhibin, calretinin, plac ental alkaline phosphatase (PLAP), and progesterone and estrogen receptors. The most consistent markers with the strongest immunoreactivity were vimen tin, AAT, NSE, and the progesterone receptor, which were each found in more than 90% of the tumors. Using immunocytochemical methods involving antigen retrieval, cytokeratin was demonstrated in almost 70% of the cases. Synapt ophysin was found in 22% of the tumors, while chromogranin was absent and t yrosine hydroxylase was only present in a few tumors. None of the other mar kers tested were expressed by SPTs. This staining pattern fails to reveal a clear phenotypic relationship with any of the defined cell lineages of the pancreas. In view of the striking female preponderance of SPTs and the kno wn close approximation of the genital ridges to the pancreatic anlage durin g embryogenesis, it is, however, hypothesized that SPTs might derive from g enital ridge/ovarian anlage-related cells, which were attached to the pancr eatic tissue during early embryogenesis.