The cancer known as melanoma begins in melanocytes, the skin cells that produce the dark protective pigment called melanin. When you're exposed to sunlight, the melanin in your skin increases to form a protective layer in the form of a suntan. Melanoma consists of melanocytes which have been transformed into cancer cells that grow uncontrollably. Melanoma cells usually still produce melanin, which is why these cancers tend to be mixed shades of tan, brown, and black.

Unlike basal cell and squamous cell carcinomas of the skin, melanoma has a strong tendency to spread to other parts of the body. Once colonies of melanoma cells reach vital internal organs and grow, they are much more difficult to treat. That is why this is a potentially lethal form of cancer.

While melanoma may suddenly appear without warning, it may also begin in or near a mole or other dark spot in the skin. That is why it's important to know the size and location of the moles on your body, so you'll recognize any changes that might take place.

One half is unlike the other half.

An irregular, scalloped, or poorly defined border.

Is varied from one area to another; has shades of tan, brown, or black; is sometimes white, red, or blue.

Melanomas usually are greater than 6mm (the size of a pencil eraser) when diagnosed, but they can be smaller.

A mole or skin lesion that looks different from the rest or is changing in size, shape, or color.

What are the warning signs of malignant melanoma?

Any one or more of these changes occurring in a new or existing pigmented (tan, brown) area of the skin, or in a mole, may indicate the presence of a malignant melanoma:

• Change in size, especially sudden or continuous enlargement
• Change in color, especially multiple shades of tan, brown, dark brown, black; the mixing of red, white and blue; or the spreading of color from the edge into the surrounding skin
• Change in shape, especially the developing of an irregular, notched border where the border used to be regular
• Change in elevation, especially the raising of a part of a pigmented area that used to be flat or only slightly elevated
• Change in surface, especially scaliness, erosion, oozing, crusting, ulceration, or bleeding
• Change in surrounding skin, especially redness, swelling, or the developing of colored blemishes next to, but not as part of, the pigmented area
• Change in sensation, especially itchiness, tenderness, or pain
• Change in consistency, especially softening or hardening

Who's at risk?

In general, the risk of developing malignant melanoma increases as people grow older. In addition, individuals living in the Sun Belt (i.e., closer to the equator) are at greater risk. Caucasians are affected ten times more frequently than Blacks. Beyond these general considerations, several specific factors identify individuals prone to develop this tumor. People at high risk are those who have:

• A family history of malignant melanoma
• Had a malignant melanoma in the past
• Unusual "dysplastic" moles (often larger than 1/4 inch, irregular in shape, and multi-colored)
• Fair skin, light hair, and light eye color, and a tendency to sunburn easily and to tan with difficulty
• Large brown moles at birth
• A record of painful or blistering sunburns, especially when young
• Indoor occupations and outdoor recreational habits
• Considerable outdoor exposure, especially while living in sunny regions

Images povided by the American Academy of Dermatology.