INFLAMMATORY MYOFIBROBLASTIC TUMOR OF THE PANCREATICOBILIARY REGION -MORPHOLOGIC AND IMMUNOCYTOCHEMICAL STUDY OF 3 CASES

Inflammatory myofibroblastic tumor (IMT) is a rare tumor of the pancre aticobiliary region. The etiology and biologic behavior of IMTs at thi s site are unknown. We present three patients with IMT of the pancreat icobiliary region, each with long-term follow-up. In all three cases a second tumor developed. Grossly these tumors mimicked a malignant pro cess. Microscopically, all were composed of an admixture of spindle ce lls and chronic inflammatory cells, including plasma cells, lymphocyte s, eosinophils, and macrophages. The spindle cells stained positively for smooth muscle actin and vimentin but were negative for S-100, cyto keratin, CD35, and latent membrane protein. Results of in situ hybridi zation with EBER probes were negative in all cases. In addition to car cinoma, 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 a ppear to be related to Epstein-Barr virus.