A renal mass in a patient with melanoma

A 61-year-old man presented to the emergency room with significant weight loss. Laboratory analysis revealed elevations in blood urea nitrogen, creatinine, and white blood cell count. Computed tomography imaging showed a large, infiltrative mass in the right renal vein, with metastasis to the brain. Biopsy of soft tissue mass and kidney revealed positive staining for malignant melanoma. Malignant melanoma to the kidney is extremely rare, and imaging modalities alone cannot differentiate neoplasms in the kidney. It is therefore necessary to use specific immunocytochemical staining along with imaging modalities to make a specific diagnosis when the primary origin of the tumor is unknown.