Based on the results of immunohistochemical staining in the case herein presented, cystic and sarcomatous renal cell carcinoma (HMB45 negative), cystic nephroma (HMB45 negative), mixed epithelial and stromal tumor (HMB45 negative), leiomyosarcoma (HMB45 negative), and melanoma (HMB45 positive, S-100 protein positive) were excluded as differential diagnoses. The gene discussed is PMEL; the disease is Cystic Nephroma.