When a Lower Abdominal Lump Turned Out to Be a Stromal Tumor of Unknown Malignant Potential

Abdominopelvic masses usually do not occur in young females and should be evaluated carefully to rule out rare smooth muscle tumors. Here, we present the case of a 23-year-old female who complained of pain in the lower abdomen, urinary frequency, constipation, and dysuria for the last two months. The examination showed a solid, immobile lower abdominal mass measuring approximately 20 × 25 cm. MRI revealed a clear-cut abdominopelvic lesion measuring 7.9 × 19.7 × 30.4 cm, and fluorodeoxyglucose-positron emission tomography depicted subtle hypermetabolic activity, indicative of a low-grade stromal lesion. During an exploratory laparotomy, a large mass arising on the right broad ligament was noted, and total excision was performed. Histopathology revealed a smooth muscle tumor with mild-to-moderate atypia, low mitotic activity, and absence of coagulative necrosis, which was consistent with a diagnosis of stromal tumor of unknown malignant potential (STUMP). The course after surgery was uneventful, and at the six-month follow-up, the patient did not show any metastasis or recurrence. This case described the diagnostic difficulties of extrauterine STUMP and the significance of histopathological verification and regular follow-up surveillance.