Melanoma of Unknown Primary Presenting as a Renal Mass: A Case Report.

Melanoma of unknown primary (MUP) is a rare presentation of melanoma most commonly found in the lymph nodes, subcutaneous tissue, and visceral organs. Renal involvement has rarely been demonstrated in the literature. We reported a 66-year-old male with an incidental finding of a small (1.7cm) right renal mass who underwent partial nephrectomy with pathology consistent with metastatic melanoma. After thorough evaluation, no primary melanotic lesion was identified, therefore characterizing his disease as MUP. The patient subsequently was treated with ipilimumab and nivolumab and is continuing on maintenance therapy with nivolumab. This case is one of three known cases of MUP presenting as a renal mass according to current literature. Though rare, this highlights the importance of including MUP in the differential diagnosis of renal masses.