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

Abstract

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.