A melanoma is a type of skin cancer that develops from the dendritic clear cells in the epidermis (the melanocytes) which produce melanin (skin pigment). Most of these cancers occur on the skin as the result of too much exposure to ultraviolet radiation from sunlight. 70% develop from an existing mole or freckle (very dark moles larger than the diameter of a pencil eraser are particularly suspect, as are irregularly-shaped moles). However, they can also develop in the eye (ocular melanoma) and, very rarely, on the mucous membranes of the mouth, nose, vagina, or anus. Some birthmarks containing congenitally mutated cells can also develop into melanomas, and thus some young children who have had little or no sun exposure can develop these cancers.
Melanoma is also known in some medical literature as melanocarcinoma and nevocarcinoma.
Melanoma cases make up only 11% of all skin cancer cases, but it is by far the deadliest form; it kills 40,000 people a year worldwide. Over 51,000 new cases are expected in the U.S. this year. Almost all skin cancer deaths are the result of melanomas.
There are three stages of melanoma:
Stage I: The cancer is confined to the epidermis and the tumor is less than 1.5 millimeters thick. Treatment generally involves surgery to remove the tumor and biopsies of nearby lymph nodes. Skin grafts may be needed.
Stage II: The cancer spreads through the epidermis and into the loose papillary dermis, but it has not moved into tissues below the skin or into the lymph nodes. The tumor is 1.5-4 millimeters thick. Treatment generally involves surgery to remove the tumor and nearby tissues and lymph nodes. Immunotherapy (also called "biological therapy"; it involves treatments with interferon or interleukin-2 to boost the immune system) or chemotherapy may also be needed. Skin grafts are necessary.
Stage III: The tumor is more than 4 millimeters thick and the cancer has spread through the papillary dermis and has metastasized into other nearby body tissues. Treatment is a more aggressive version of the treatment for Stage II.
Stage IV: The cancer has spread to other organs or lymph nodes throughout the body. Treatment involves surgery and chemotherapy and sometimes radiation therapy.
Stage III and IV melanomas can kill a person very quickly. My father did a stint in the Air Force as a base physician, and one day a young, tanned airman asked him to take a look at a mole on the back of his neck beneath his collar. When the airman took off his shirt, my dad said, "It was like opening a kitchen cabinet to see a black widow spider inside -- I just went cold at the sight of the thing." The young man had a shiny, blue-black melanoma the size of a quarter on his neck. My father told him to go to the hospital immediately, but it was too late; the airman died just a few months later.
On the plus side, betulinic acid, a extract from birch tree bark, has shown promise as a non-toxic treatment for melanomas.
Also, in June of 2002, scientists from the Cancer Genome Project (a child organization of the Human Genome Project) announced that they discovered that 70% of all melanoma cases involve a mutation to a gene named B-RAF, which is one of a series of genes that must all be switched on for a cell to grow and divide. Researchers believe that drugs designed to switch this gene off may provide a better future treatment for melanoma.
Some of this writeup is based on work I did for the science dictionary at http://biotech.icmb.utexas.edu/.