Melanoma is an aggressive malignancy of pigment-producing cells known as melanocytes. Melanoma may arise at sites of melanocytes including on the skin, mucous membranes, around the nail apparatus, and in the eye.

Melanomas can be found anywhere on the body, including the glans penis, foreskin, shaft, anus (see anorectal melanoma), urethra, and the scrotum. Primary melanomas of the glans penis and male urethra are rare, representing < 0.1% of all melanomas. Anogenital melanoma is responsible for approximately 0.05% of all colorectal malignancies and 1% of all anal canal cancers. Scrotal melanomas are equally as rare. Melanomas of the genitalia most often arise de novo in elderly individuals.

The best prognostic indicator is the Breslow thickness, a measure of the depth of invasion of the melanoma. Lesions less than 0.75 mm in thickness generally have a good prognosis, while lesions greater than 3.5 mm have a very poor prognosis. A higher percentage of male genitourinary melanomas than cutaneous melanomas are at an advanced stage at the time of diagnosis, either as a result of late presentation (urethral melanoma) or delay in seeking medical care, leading to a poorer outcome. Urethral melanomas, especially, have a worse prognosis than cutaneous melanoma.

There are no established guidelines for staging of mucosal melanoma and scrotal melanoma. For glans and penile melanoma, both the American Joint Committee on Cancer (AJCC) staging criteria and a 3-stage system have been used:

Stage 1: Lesion is confined to the penis.
Stage 2: Metastatic to the regional lymph nodes.
Stage 3: Disseminated disease.