ALK-negative retroperitoneal inflammatory myofibroblastic tumor treated conservatively: case report.

A 55-year-old female presented with left flank pain and ureteral obstruction. Imaging revealed a retroperitoneal mass suspicious for malignancy. Histopathology confirmed an inflammatory myofibroblastic tumor (IMT; anaplastic lymphoma kinase [ALK]-negative, mouse double minute 2 homolog-positive). Due to vascular encasement prohibiting safe resection, cystoscopic ureteral stenting was performed followed by 12 months of prednisone and celecoxib therapy. Serial imaging showed progressive regression, with near-resolution at 36 months. This demonstrates successful medical management of unresectable ALK-negative retroperitoneal IMT.