Urinary Bladder Inflammatory Myofibroblastic Tumor with Mutated TP53 and PPFIBP1-ALK Gene Fusion

Inflammatory myofibroblastic tumor (IMT) is a mesenchymal neoplasm with distinct histologic features. Approximately 50%of these tumors harbor ALK gene rearrangements with multiple gene fusion partners described, a fewof which are predictive of poor prognosis. One example is the ALK-RANBP2 gene rearrangement identified in cases of epithelioid myofibroblastic sarcomas. Many studies have attempted to identify other immunohistochemical or molecular features, which may be predictive of outcome, with conflicting results, particularly regarding the expression of p53. In addition, aberrant p53 expression may be used to favor a diagnosis of leiomyosarcoma over IMT.We present the case of a deeply invasive urinary bladder IMT with aberrant p53 expression and corresponding TP53 genomic alteration, the latter previously reported in only 2 unrelated cases of malignancy. Our case highlights that p53 aberrant expression and TP53 genomic alterations may be found in IMTs andmay be related to IMTpathogenesis and prognosis. Furthermore, relying on absence of aberrant p53 expression in IMT in order to distinguish it from histologic mimickers may lead to potential diagnostic pitfalls. In addition, our case demonstrated weak immunohistochemical staining for ALK and was found to harbor a PPFIBP1-ALKgene fusion, previously described in only 2 reports of IMTs of the lung, also with associated negative or weak immunohistochemical staining for ALK.