malignant tumor of the skin. The most common types of skin cancer are basal cell carcinoma, squamous cell carcinoma, and melanoma. Rarer forms include mycosis fungoides (a type of lymphoma) and Kaposi's sarcoma. Overexposure to the sun is the primary cause of the common skin cancers, and the popularity of tanning since the 1930s lies behind the rise in skin cancer rates. The depletion of the earth's protective ozone layer also plays a role. The most effective way of preventing skin cancer is to avoid exposure to the sun's ultraviolet rays by consistently applying effective sunscreens (see sunburn) and wearing protective clothing.

Basal and Squamous Cell Carcinomas

Basal and squamous cell carcinomas are the most common types of cancer. Both arise from epithelial tissue (see epithelium). They are rare in dark-skinned people; light-skinned, blue-eyed people who do not tan well but who have had significant exposure to the rays of the sun are at highest risk. Both types usually occur on the face or other exposed areas.

Basal cell carcinoma typically is seen as a raised, sometimes ulcerous nodule. The nodule may have a pearly appearance. It grows slowly and rarely metastasizes (spreads), but it can be locally destructive and disfiguring. Squamous cell carcinoma typically is seen as a painless lump that grows into a wartlike lesion, or it may arise in patches of red, scaly sun-damaged skin called actinic keratoses. It can metastasize and can lead to death.

Basal and squamous cell carcinomas are easily cured with appropriate treatment. The lesion is usually removed by scalpal excision, curettage, cryosurgery (freezing), or micrographic surgery in which successive thin slices are removed and examined for cancerous cells under a microscope until the samples are clear. If the cancer arises in an area where surgery would be difficult or disfiguring, radiation therapy may be employed. Genetic scientists have discovered a gene that, when mutated, causes basal cell carcinoma.

Melanoma

Melanoma is the most virulent type of skin cancer and the type most likely to be fatal. As with the other common skin cancers, melanoma can be caused by exposure to the sun, and its incidence is increasing around the world. There also appears to be a hereditary factor in some cases. Although light-skinned people are the most susceptible, melanomas are also seen in dark-skinned people. Melanomas arise in melanocytes, the melanin-containing cells of the epidermal layer of the skin. Melanin is the pigment that gives skin color and that helps to protect the skin from sun damage. In light-skinned people, melanomas appear most frequently on the trunk in men and on the arms or legs in women. In blacks melanomas appear most frequently on the hands and feet. It is unknown whether melanoma in blacks is related to sun exposure. It is recommended that people examine themselves regularly for any evidence of the characteristic changes in a mole that could raise a suspicion of melanoma. These include asymmetry of the mole, a mottled appearance (variations in color from shades of brown to a bluish tint), irregular or notched borders, and oozing or bleeding or a change in texture. Surgery performed before the melanoma has spread is the only effective treatment for melanoma.

Bibliography

See publications of the National Cancer Institute and the American Cancer Society.

The Columbia Encyclopedia, Sixth Edition Copyright© 2004, Columbia University Press. Licensed from Lernout & Hauspie Speech Products N.V. All rights reserved.

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