Solid-pseudopapillary tumor of the pancreas: its origin revisited

Solid-pseudopapillary tumor of the pancreas (SPT) has distinctive morphologic and biologic features but an unclear origin. It is classified among the pancreatic epithelial tumors, though many are reported to be negative for cytokeratin. Also unclear are its neuroendocrine differentiation, its capability to express alpha-1-antitrypsin (AAT) and, in view of the tumor's striking prevalence in women, its relationship with the female genital tract. To clarify these issues, the immunoprofiles of 59 SPTs were defined by applying a battery of antibodies against cytokeratin, vimentin, neuron-specific enolase (NSE), synaptophysin, chromogranin A, tyrosine hydroxylase (TH), AAT, LeuM1, Ki-M1P, smooth-muscle actin, CD34, alpha-inhibin, calretinin, placental alkaline phosphatase (PLAP), and progesterone and estrogen receptors. The most consistent markers with the strongest immunoreactivity were vimentin, 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. Synaptophysin was found in 22% of the tumors, while chromogranin was absent and tyrosine hydroxylase was only present in a few tumors. None of the other markers 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 known close approximation of the genital ridges to the pancreatic anlage during embryogenesis, it is, however, hypothesized that SPTs might derive from genital ridge/ovarian anlage-related cells, which were attached to the pancreatic tissue during early embryogenesis.