Melanoma is a form of skin cancer that develops when DNA damage to skin melanocytes occurs. These are the pigment producing cells of our skin.
This most often is caused by ultraviolet radiation from sunshine or tanning beds which triggers mutations (genetic defects) causing the cells to multiply rapidly and form malignant tumors. These tumors originate in the basal layer of the epidermis.
Melanomas often resemble moles; some develop from moles. The majority of melanomas are black or brown, but they can also be skin-colored, pink, red, purple, blue or white.
Melanoma is caused mainly by intense, occasional UV exposure (frequently leading to sunburn), especially in those who are genetically predisposed to the disease. Melanoma kills an estimated 9,710 people in the US annually.
If melanoma is recognized and treated early, it is almost always curable, but if it is not, the cancer can advance and spread to other parts of the body, where it becomes hard to treat and can be fatal. While it is not the most common of the skin cancers, it causes the most deaths. The American Cancer Society estimates that at present, more than 120,000 new cases of melanoma in the US are diagnosed each year.
For more information look here: http://www.skincancer.org/skin-cancer-information/melanoma