Pediatric inflammatory myofibroblastic tumor of the bladder with ALK–FN1 fusion successfully treated by alectinib

An inflammatory myofibroblastic tumor (IMT) is a mesenchymal neoplasm characterized by the proliferation of myofibroblasts and inflammatory cell infiltration. Although radical resection is the only established treatment strategy for IMT, it can cause functional disorders when vital organs are affected. We describe a case of pediatric IMT of the bladder with FN1–ALK (fibronectin 1–anaplastic lymphoma kinase) fusion. Radical resection might lead to urinary disturbance due to the large tumor size at diagnosis. However, the tumor was successfully treated with alectinib, a second‐generation ALK inhibitor, followed by transurethral resection of the bladder tumor without any complications.