Stromal hyalinization within pseudopapillary structures. Stroma is usually imperceptible, but it can be hyalinized or myxoid (PAS +, diastase resistant).
About the Disease
Solid pseudopapillary tumor (SPT) of pancreas is a rare tumor of low malignant potential that occurs predominantly in adolescent girls and young women (mean age: 28 years). It consists of poorly cohesive monomorphic epithelial cells arranged in solid sheets as well as pseudopapillary structures, along with areas of hemorrhage and pseudocystic changes. The histogenesis of SPT is unknown. It expresses epithelial, mesenchymal, and neuroendocrine markers. The differential diagnosis includes low-grade neuroendocrine tumor and pancreatoblastoma. Almost 90% of cases have point mutation in exon 3 of CTNNB1 which lead to nuclear accumulation of β-catenin as well as lymphoid enhancer-binding factor 1 (LEF1), which can be demonstrated immunohistochemically. There is complete loss (or nuclear localization) of E-cadherin expression.
The biologic behavior is benign in 80-90% of cases. Overall survival rate is >90%. Even patients with recurrence or metastasis have prolonged survival. There are no histologic criteria that can reliably predict malignant behavior; however, certain features are more frequently associated with risk of metastasis.