Skin Cancer

Skin Cancer

Skin Cancer, malignancy in the skin, and the most common of all cancers. There are three main types of skin cancer: basal cell carcinoma, squamous cell carcinoma, and melanoma. Basal cell carcinoma, the most common type, develops in the basal, or bottom, layer of the epidermis, the top layer of skin. Squamous cell carcinoma, the second most common type, develops in the upper layers of the epidermis. The American Cancer Society estimates that basal cell and squamous cell skin cancers account for more than 1.3 million new cases each year, but for only 1,900 deaths. In Canada, 68,000 new cases of basal cell and squamous cell skin cancer is diagnosed each year.

The third type of skin cancer is melanoma. It develops in the melanocytes, or pigment cells, which are found throughout the basal layer. Melanoma is the most dangerous type of skin cancer and is responsible for about three-quarters of all skin cancer deaths. About 48,000 new cases of melanoma are diagnosed annually in the United States, and an estimated 7,700 people die from this disease each year. The incidence of melanoma has been increasing faster in the United States than any other form of cancer, and a person born in the early 1990s is 12 times more likely to develop melanoma than a person born in the early 1940s. In Canada, about 3,100 new cases of melanoma are diagnosed each year.


RISK FACTORS

Skin cancers can grow in any part of the skin, but approximately 90 percent develop in areas exposed to the sun, especially the face, neck, backs of the hands, and the scalps of bald men. Exposure to direct sunlight, especially during childhood, is the chief risk factor for skin cancer, and the greater the number of blistering sunburns a person has had, the greater the risk of developing skin cancer later in life. People with pale skin are at greatest risk for skin cancer, particularly if their skin burns or freckles easily.
A family history of skin cancer can also increase a person’s risk. Studies are in progress to determine which individuals are genetically predisposed to the disease. In 1996, for example, scientists reported the discovery of a gene they believe causes basal cell carcinoma. The gene, called patched or PTC, helps control cell growth and development. If the gene is missing, defective, or damaged by ultraviolet radiation, unrestrained cell proliferation may result. Another aberrant gene, called multiple tumor suppressor (MTS1), has also been linked to melanoma.
Diet may also play a role. A recent study found that patients on a diet of 20 percent fat had fewer precancerous growths and non-melanoma skin cancers than those who ate a normal diet of about 38 percent fat.


SYMPTOMS AND DIAGNOSIS

Early detection and treatment are the keys to survival, especially for melanoma. Any of several skin changes may signal skin cancer and should be reported to a physician. These include any change in the size, shape, color, or texture of a mole or other darkly pigmented area; any mole that begins to itch or becomes tender; the development of a new mole or other growth, particularly if it feels hard; any mole or other growth that spontaneously or persistently bleeds; a skin ulcer that does not heal; and a black spot under a toenail or fingernail that extends beneath the cuticle. To confirm a diagnosis a physician may perform a biopsy, removing a small piece of the skin to examine under a microscope for the presence of cancerous cells.


TREATMENT

Although skin cancer is the most common cancer in the United States, it is also the most curable, especially when detected early. One of several surgical methods is used to remove the cancerous tissue. In some cases, the tissue is destroyed through the application of intense cold (cryosurgery). In advanced cases, surgical removal of the tissue coupled with radiation, chemotherapy, or both may be required.

A class of vitamin-based drugs called retinoids have been shown to reduce the number of basal cell and squamous cell carcinomas. However, the drugs can cause liver abnormalities, bone problems, fetal malformation, and other undesirable side effects.
Potential skin cancer treatment studies now underway include the use of the drugs interleukin-2 and interferon. A vaccine to reduce the recurrence of melanoma has shown promise in early tests.


PREVENTIVE MEASURES

Sunlight that reaches the earth’s surface contains two kinds of ultraviolet (UV) radiation. UV-A and UV-B both contribute to sunburn and skin cancer, as well as to conditions such as premature wrinkling of the skin. The U.S. Environmental Protection Agency has determined that depletion of the ozone layer in the upper atmosphere will continue to increase radiation damage to skin and skin cancer rates in the future.

The Skin Cancer Foundation recommends that people avoid the sun at its peak (from 10 am to 4 pm), seek shade, and cover up with clothing and a brimmed hat. It also recommends the regular use of sunscreen, which has been shown to prevent the development of precancerous keratoses (skin lesions that appear during middle age) and decrease the risk of skin cancer. Because skin cancer develops slowly over many years, it is important that protection from too much sun begin in childhood. Indoor tanning parlors should also be avoided, since they expose people to the same kinds of ultraviolet radiation as sunlight. Learning to identify early signs of skin cancer is crucial, as is periodic self-examination of the skin. Any skin changes or abnormalities should be reported to a physician.