Melanoma, the most serious form of skin cancer, is not as common as the other two major types of skin cancer (basal cell and squamous cell carcinomas). The number of new cases of melanoma diagnosed each year in the United States has more than doubled, however, in the past three decades.
The lifetime melanoma risk for the average American is about 1 percent. However, for some people a combination of genetics, environment, and lifestyle can significantly increase the risk of developing melanoma. Invasive melanoma currently accounts for more than 53,000 new cases in the United States annually.
Melanoma begins in melanocytes, the cells in the epidermal layer of the skin that produce the pigment melanin. Melanin in normal melanocytes produces "tan" skin as a response to damage from UV light.
Melanoma can arise by several routes. It may arise directly from a melanocyte. Sometimes, the melanocyte first turns into a normal mole (also called a nevus) or an irregular mole (a dysplastic nevus), which then becomes cancerous. Melanocytes can also be found in internal organs, where they may become cancerous on occasion.
Melanomas often look asymmetrical, have a ragged or blurred border, and are dark in color. Although they are usually wider than a pencil eraser, with improved surveillance physicians are now detecting smaller melanomas.
Melanomas are cancerous, but the large majority do not spread right away. Many begin as a "melanoma in situ." During that stage, the growth does not venture beyond the very most superficial layer of skin, the epidermis.
In a second stage, melanoma can penetrate the lower layer of the skin, the dermis. If the melanoma penetrates very deeply into the dermis, it may progress to a vertical growth phase -- in which it can metastasize, or spread throughout the body. Although melanoma usually shows up on the trunk, the arms and legs, it can develop on any part of the body -- including those never exposed to the sun.
Melanoma of the Eye
The eye is the second most common site in the body for melanomas after skin. However, with only 2,500 cases a year, these ocular melanomas are relatively rare and require special techniques for diagnosis and treatment.
Although children are usually born without nevi in the eye, ultimately more than 10 percent of the population will develop a nevus in the eye. The incidence of nevi in the eye is higher in whites than in African Americans or Asians. Perhaps one in 5,000 of these undergoes malignant transformation. This is usually easy to detect by experienced ophthalmic oncologists.
Untreated ocular melanomas may spread through the blood stream, lodge in the liver and cause death. At Memorial Sloan-Kettering we have a team of dedicated and experienced clinicians to assist in all phases of the disease.
Ocular melanomas may be found in the uveal tract (the vascular middle layer of the eye made up of the iris, ciliary body, and choroid), conjunctiva, lid or orbit of the eye. Uveal melanomas may involve the iris, choroid and ciliary body. Melanomas of the iris have the best prognosis, whereas those of the ciliary body have the worst prognosis.
