Primary Retroperitoneal Smooth Muscle Tumor of Uncertain Malignant Potential (STUMP): A Diagnostic Enigma.

Retroperitoneal sarcomas represent a group of rare malignant neoplasms with complex clinical management and often a poor prognosis. An elderly male presented with a slowly progressive, right-sided abdominal lump for four months associated with loss of appetite and abdominal discomfort. Abdominal examination revealed an apparent retroperitoneal lump in the right lumbar and umbilical region, which was well-defined, and firm in consistency with the bosselated surface. Contrast-enhanced computed tomography (CECT) of the abdomen and pelvis revealed a heterogenous lobulated malignant appearing retroperitoneal lesion arising from the right anterior perirenal space with a differential of retroperitoneal sarcoma. Wide local excision of the tumor was done. Histopathology of the lesion revealed a smooth muscle tumor of uncertain malignant potential (STUMP). The patient is asymptomatic and recurrence-free after 24 months of follow-up.