Mesenchymal Neoplasms of the Pancreatobiliary Tract.

CONTEXT.—: Mesenchymal neoplasms of the pancreatobiliary tract are extremely rare, with most representing secondary involvement or metastatic disease. A wide range of primary benign and malignant mesenchymal neoplasms can arise in the pancreatobiliary tract. This includes the newly proposed entity, sclerosing epithelioid neoplasm of the pancreas. Thus, appropriate classification and diagnosis are essential. OBJECTIVE.—: To review the array of primary benign and malignant mesenchymal neoplasms arising in the pancreatobiliary tract, with discussion of clinicopathologic features, including morphology, immunohistochemistry, and molecular characteristics, as applicable for select tumors. DATA SOURCES.—: Literature review of published studies. CONCLUSIONS.—: When faced with a primary mesenchymal neoplasm of the pancreas, most are benign, most often representing a schwannoma, followed by inflammatory myofibroblastic tumor, and solitary fibrous tumor. If malignant, leiomyosarcoma has been the most frequently reported entity. Sclerosing epithelioid neoplasm may be considered in cases with distinct histologic features and appropriate diagnostic workup as described. In the gallbladder and biliary tract, the most common entities encountered include granular cell tumor, schwannoma, and inflammatory myofibroblastic tumor.