Inflammatory Myofibroblastic Tumor of the Bladder. How Does it Relate to Other Lesions With this Name?

Background: Pulmonary lesions called “inflammatory pseudotumors” were known for many years and were regarded as part of a spectrum of lesions called “plasma cell granulomas” (1-5) Various terms were applied: inflammatory pseudotumor, plasma cell granuloma, plasma cell pseudotumor, xanthomatous pseudotumor, pseudosarcomatous myofibroblastic proliferation, and inflammatory myofibrohistiocytic proliferation (6). Subsequently, similar tumors were described in the abdomen and other soft tissue sites (6, 7). As we have learned more about a wide spectrum of lesions in this family of myofibroblastic proliferations in a host of anatomic sites(8-16), questions concerning their etiology and biologic potential remain. Advances in understanding of the molecular biology of these tumors, launched by the discovery of a “hot spot” at 2p23 flanking the ALK gene by Griffin et al(17), have provided some insights, but other questions remain unanswered. Following the report by Griffin and her colleagues (17) of these alterations in soft tissue lesions, other investigators confirmed similar alterations in other sites, including the lung, the classic site(18). Immunohistochemistry for the protein product confirmed protein expression in subsets of these lesions in a range of anatomic sites (15, 16, 19-26), although Cessna et al noted that this staining was not wholly specific (25). These tumors have been linked, on the one hand, to nodular fasciitis (27), and, on the other hand, to cells of the accessory immune system that have been variously called fibroblastic reticulum cells, myoid cells, and dictyocytes (28).