S3772 Uterine Spindle Cell Sarcoma Presenting With Lower Gastrointestinal Bleeding: A Case Report

Introduction: Uterine sarcomas are rare aggressive malignancies, accounting for fewer than 1% of uterine cancers. Among their histologic variants, spindle cell sarcomas are particularly uncommon and aggressive. These tumors typically present with gynecologic symptoms, such as abnormal uterine bleeding or pelvic pain. However, in rare cases, they may present with atypical features like lower gastrointestinal (GI) bleeding, which may mislead clinicians into suspecting primary GI malignancy. Case Description/Methods: A 79-year-old woman with a history of hypertension and paroxysmal atrial fibrillation presented with a 6-month history of intermittent lower GI bleeding, significant weight loss, constipation, and generalized fatigue. A colonoscopy revealed a partially circumferential, ulcerated, and fungating mass in the sigmoid colon, approximately 26 cm from the anal verge. Biopsies revealed a high-grade, poorly differentiated spindle cell malignancy. Immunohistochemistry demonstrated tumor cell positivity for GATA3, PAX8 (weak to moderate), beta-catenin, MDM2, and calretinin, and negativity for CK20, CDX2, and BAP1, which supported a diagnosis of uterine spindle cell sarcoma. Computed tomography imaging identified a large pelvic mass involving the uterus and sigmoid colon, with possible fistulous communication and compression of the left ureter causing hydronephrosis. A right adrenal nodule was also noted. The tumor was deemed unresectable, and palliative chemotherapy was initiated. Discussion: Spindle cell sarcomas are highly aggressive and often present diagnostic challenges due to their atypical presentations and overlap with other malignancies. GI bleeding as a presenting symptom is rare and usually results from tumor invasion of adjacent structures. IHC plays a vital role in determining tumor origin, particularly with positive markers such as PAX8 and GATA3 that confirm Müllerian derivation. Cross-sectional imaging helps assess tumor extent and surgical feasibility.