Malignant melanoma is a serious type of skin cancer that can affect the legs and feet, as well as other parts of the body. In this disease, pigment-producing cells (melanocytes) become cancerous and grow and divide at an uncontrolled rate. The primary risk factor for malignant melanoma is exposure to ultraviolet radiation (UV rays); the mechanism by which UV rays cause melanoma is unknown.
Melanoma is less common than other types of skin cancer (e.g., basal cell carcinoma, squamous cell carcinoma), but it is more likely to spread (metastasize) via cells that break away from the original tumor, travel through the blood or lymphatic vessels, and grow within other parts of the body.
Overall, melanoma affects men and women equally. It usually develops after age 50, although it can develop at any age and on any part of the body. Light-skinned people are more likely to develop melanoma than dark-skinned people.
Each year, about 4% of new skin cancer cases are malignant melanomas. Incidence is increasing dramatically among light-skinned people throughout the world. In the United States, most cases occur in Caucasians, and worldwide, approximately 40% of cases occur in non-white populations. Melanoma causes nearly 80% of skin cancer deaths.
Approximately 35,000 new cases of melanoma are reported annually to cancer registries in hospitals in the United States. This figure underestimates the actual number of cases, because many physicians treat skin cancer in their offices. One study suggests that the actual number of cases is closer to 90,000 per year.
Annual incidence of malignant melanoma is increasing faster than any other type of cancer. Since 1973, incidence has increased from 6 to 13 cases per 100,000 people each year. The melanoma death rate also has increased over the last 50 years and according to the American Cancer Society (ACS), about 7,300 people in the United States died from the disease in 1999.
The skin is the largest organ of the human body and serves many vital purposes. It protects the body, regulates body temperature, stores water and fat, manufactures essential vitamin D, and contains nerve endings that sense the environment and relay important messages to the brain.
The skin is made up of the the thin outer surface (epidermis) where the pigment-producing melanocyte cells are located, and the thicker, underlying layer where sensory receptors, hair follicles, and sweat glands are located (dermis). The epidermis is a coat of cells that are constantly being shed and replaced with cells from the base of the epidermis. The new cells push up from the base to the surface, where they die, flake off, and are replaced by newer cells. Melanoma originates in the melanocytes of the epidermis.
Dark pigment (melanin) produced by melanocytes is one of the most important components of skin color. Other cells produce a range of other pigments, and thickness of the skin also modifies skin color, but melanin is the main factor. It ranges in color from yellow to black. Melanin also protects the body from ultraviolet light. When exposed to sunlight, melanins darken, resulting in a tanned appearance.
A common sign of melanoma is a change in the appearance of a mole. Ordinary moles, or "nevi," usually are evenly colored (brown, black, tan), round "spots" on the skin. They can be present at birth, or they may appear at any time during a person's life, often after periods of sun exposure. Most are small (less than 6 millimeters in diameter). They do not change in size or shape, although they may fade somewhat in older individuals.
Melanoma usually begins as an abnormal mole. To distinguish a normal mole from a melanoma, skin disease specialists (dermatologists) have developed the ABCD rule. According to this guide, the following features characterize melanoma:
Not all melanomas have features defined by the ABCD rule, so any new, colored growths, or changes in existing moles or lesions should be reported to a skin specialist (dermatologist) as soon as possible. Skin cancer rarely is painful, so do not wait to call a physician if the lesion does not "hurt."
Other standard warning signs of melanoma include a change in color from black or brown to white, red, or blue and a mole that becomes raised or papular (solid, elevated lesion).
Malignant melanomas of the lower extremities usually occur on the soles of the feet, in the spaces between the toes, and in the areas around the nails.
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