Smooth Muscle Tumor of Uncertain Malignant Potential Masquerading as Sarcoma.

BACKGROUND: Smooth muscle tumor of uncertain malignant potential (STUMP) is a rare uterine neoplasm with histopathological features intermediate between benign leiomyoma and leiomyosarcoma, posing significant diagnostic and management challenges. CASE PRESENTATION: A 41-year-old woman presented with abdominal pain and distension. Examination revealed a large abdominal mass occupying all quadrants. MRI demonstrated a 20 × 18 × 16 cm exophytic sub-serosal fundal mass extending to the epigastrium, with extensive cystic degeneration suggestive of sarcomatous change. She underwent exploratory laparotomy with total abdominal hysterectomy and bilateral salpingo-oophorectomy. Intraoperatively, a large uterine fundal mass with extensive neovascularization was identified. Final histopathological examination and immunohistochemistry confirmed the diagnosis of STUMP. CONCLUSION: This case highlights the difficulty in preoperative differentiation between benign leiomyomas and premalignant or malignant uterine smooth muscle tumors. Definitive diagnosis relies on histopathological and immune-histochemical assessment, underscoring the importance of appropriate surgical management and long-term surveillance in patients diagnosed with STUMP.