Skin cancer is the most common cancer of all when cases of the highly curable forms are included in the count. Of the more than 1 million cases of skin cancer diagnosed each year, about 77,000 are of the most serious type, melanoma. Almost all cases of skin cancer can be traced to excessive exposure to ultraviolet (UV) radiation from the sun, including longer-wavelength ultraviolet A (UVA) and shorter-wavelength ultraviolet B (UVB) radiation. UVB radiation causes sunburns and can damage the eyes and immune system. UVA is less likely to cause an immediate sunburn, but it damages connective tissue and leads to premature aging of the skin. Tanning lamps and tanning salon beds emit mostly UVA radiation. Both solar and artificial sources of UVA and UVB radiation are human carcinogens that cause skin cancer.
Both severe, acute sun reactions (sunburns) and chronic low-level sun reactions (suntans) can lead to skin cancer. According to the American Academy of Dermatology, the risk of skin cancer doubles in people who have had five or more sunburns in their lifetime. People with fair skin have less natural protection against skin damage from the sun and a higher risk of skin cancer than people with naturally dark skin. Severe sunburns in childhood have been linked to a greatly increased risk of skin cancer in later life, so children in particular should be protected. Other risk factors include having many moles (particularly large ones), spending time at high altitudes, and having a family history of the disease.
Skin Cancer Photo Gallery
There are three main types of skin cancer, named for the types of skin cell from which they develop. Basal cell and squamous cell carcinomas together account for about
Pap test A scraping of cells from the cervix for TERMS examination under a microscope to detect cancer.
Melanoma A malignant tumor of the skin that arises from pigmented cells, usually a mole.
Ultraviolet (UV) radiation Light rays of a specific wavelength, emitted by the sun; most UV rays are blocked by the ozone layer in the upper atmosphere.
Basal cell carcinoma Cancer of the deepest layers of the skin.
Squamous cell carcinoma Cancer of the surface layers of the skin.
Sunscreen protects against skin cancer as well as sunburns.
95% of the skin cancers diagnosed each year. They are usually found in chronically sun-exposed areas, such as the face, neck, hands, and arms. They usually appear as pale, waxlike, pearly nodules, or red, scaly, sharply outlined patches. These cancers are often painless, although they may bleed, crust, and form an open sore.
Melanoma is by far the most dangerous skin cancer because it spreads so rapidly. It can occur anywhere on the body, but the most common sites are the back, chest, abdomen, and lower legs. A melanoma usually appears at the site of a preexisting mole. The mole may begin to enlarge, become mottled or varied in color (colors can include blue, pink, and white), or develop an irregular surface or irregular borders. Tissue invaded by melanoma may also itch, burn, or bleed easily.
To protect yourself against skin cancer, avoid overexposure to UV radiation. People of every age, including babies and children, need to be protected from the sun (see the box “Sunscreens and Sun-Protective Clothing”). You can help with early detection by examining your skin regularly. Most of the spots, freckles, moles, and blemishes on your body are normal, but if you notice an unusual growth, discoloration, or sore that does not heal, see your physician or a dermatologist immediately. The characteristics that may signal that a skin lesion is a melanoma are illustrated in Figure 12.4.
To see a variety of photos of melanoma and benign moles, visit the National Cancer Institute’s Visuals Online site (http://visualsonline.cancer.gov).
If you have an unusual skin lesion, your physician will examine it and possibly perform a biopsy. If the lesion is cancerous, it is usually removed surgically, a procedure that can almost always be performed in the physician’s office using a local anesthetic. Treatment is usually simple and successful when the cancer is caught early. Even for melanoma, the outlook after removal in the early stages is good, with a five-year survival rate of 98% if the tumor is localized but only 62% if the cancer has spread to adjacent lymph nodes. Most melanomas are detected in the early, localized stage.
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