Malignant mixed epithelial and stromal tumor of the kidney with rhabdomyosarcomatous transformation presenting with gross hematuria.

Malignant rhabdomyosarcoma associated with mixed epithelial and stromal tumor of the kidney (MESTK) is an exceptionally rare clinical phenomenon, with only two reported cases. Here, we describe the case of a middle-aged Middle Eastern woman with a left renal mass diagnosed as malignant MESTK with rhabdomyosarcomatous transformation. The patient initially presented with gross hematuria and was found to have a heterogenous 6.3 × 4.0 cm left renal mass, initially suspected to be renal cell carcinoma. She underwent nephrectomy with surgical resection of the tumor. Microscopic exam revealed neoplastic tissue composed of spindle and epithelial cells. The immunohistochemical analysis revealed positive staining for desmin, SMA, PR and negative staining for EMA, HMB 45, Melan A, and ER, consistent with MESTK with malignant rhabdomyosarcomatous transformation. The patient's whole-body positron emission tomography/computed tomography revealed no residual malignancy, and the patient currently remains under clinical observation.