Pelvic ALK-Positive Inflammatory Myofibroblastic Tumor Presenting 8 Years After Uterine Smooth Muscle Tumor of Uncertain Malignant Potential.

Inflammatory myofibroblastic tumor (IMT) is a rare mesenchymal neoplasm with intermediate biologic potential that rarely involves the female genital tract. Distinguishing IMT from other pelvic spindle cell tumors can be challenging, particularly in patients with a prior history of uterine smooth muscle neoplasms. We report a 59-year-old woman who underwent hysterectomy for a smooth muscle tumor of uncertain malignant potential and presented 8 years later with recurrent small bowel obstruction and right flank pain. Imaging revealed a large infiltrative pelvic mass involving ovaries, ureter, small bowel, peritoneum, and iliac vessels. She underwent extensive multidisciplinary surgery, including small bowel resection, right nephrectomy, and vascular reconstruction. Histopathologic examination demonstrated a fascicular proliferation of spindle cells associated with a prominent lymphoplasmacytic inflammatory infiltrate. Diffuse anaplastic lymphoma kinase (ALK) expression was identified by immunohistochemistry, and fluorescence in situ hybridization demonstrated an ALK rearrangement, supporting the diagnosis of ALK-positive IMT. Identification of the ALK rearrangement directly influenced treatment selection and enabled initiation of ALK-targeted therapy. This case highlights the diagnostic challenges posed by pelvic spindle cell neoplasms in a patient with a history of uterine smooth muscle neoplasms and underscores the importance of integrating morphologic, immunohistochemical, and molecular findings to establish an accurate diagnosis and guide targeted therapy.