Inflammatory myofibroblastic tumor of the pancreaticobiliary region: morphologic and immunocytochemical study of three cases.

Inflammatory myofibroblastic tumor (IMT) is a rare tumor of the pancreaticobiliary region. The etiology and biologic behavior of IMTs at this site are unknown. We present three patients with IMT of the pancreaticobiliary region, each with long-term follow-up. In all three cases a second tumor developed. Grossly these tumors mimicked a malignant process. Microscopically, all were composed of an admixture of spindle cells and chronic inflammatory cells, including plasma cells, lymphocytes, eosinophils, and macrophages. The spindle cells stained positively for smooth muscle actin and vimentin but were negative for S-100, cytokeratin, CD35, and latent membrane protein. Results of in situ hybridization with EBER probes were negative in all cases. In addition to carcinoma, the differential diagnosis of these tumors includes follicular dendritic cell tumor and inflammatory fibrosarcoma. The importance of extensive pathologic examination to prevent misdiagnosis and the need for long-term follow-up are emphasized. This subset of IMT does not appear to be related to Epstein-Barr virus.