Viagra® (Sildenafil) was approved by the FDA in 1998 for the treatment of erectile dysfunction. Viagra® is a PDE5 enzyme inhibitor – which affects the same cell-signaling pathways that melanoma cells use to metastasize. Melanoma is a dangerous form of skin cancer that develops in the melanocytes, the melanin-producing cells located in the bottom layer of the epidermis. The American Cancer Society estimates that over 57,000 men will be diagnosed with melanoma annually, with an average age of diagnosis around age 63.