Melanoma is a type of skin cancer that begins in melanocytes. It is potentially dangerous because it can invade nearby tissues and spread to other parts of the body, such as the lung, liver, bone, or brain through a process called metastasis. The earlier that melanoma is detected and removed, the more likely that treatment will be successful.
Most melanocytes are in the skin, and melanoma can occur on any skin surface. It can develop from a common mole or dysplastic nevus, and it can also develop in an area of apparently normal skin. In addition, melanoma can also develop in the eye, the digestive tract, and other areas of the body.
When melanoma develops in men, it is often found on the head, neck, or back. When melanoma develops in women, it is often found on the back or on the lower legs.
People with dark skin are much less likely than people with fair skin to develop melanoma. When it does develop in people with dark skin, it is often found under the fingernails, under the toenails, on the palms of the hands, or on the soles of the feet.
Often the first sign of melanoma is a change in the shape, color, size, or feel of an existing mole. Melanoma may also appear as a new colored area on the skin.
The ABCDE rule describes the features of early melanoma :
- Asymmetry. The shape of one half does not match the other half.
- Border that is irregular. The edges are often ragged, notched, or blurred in outline. The pigment may spread into the surrounding skin.
- Color that is uneven. Shades of black, brown, and tan may be present. Areas of white, gray, red, pink, or blue may also be seen.
- Diameter. There is a change in size, usually an increase. Melanomas can be tiny, but most are larger than 6 millimeters wide (about 1/4 inch wide).
- Evolving. The mole has changed over the past few weeks or months.
Melanomas can vary greatly in how they look. Many show all of the ABCDE features. However, some may show only one or two of the ABCDE features. However, some may show only one or two of the ABCDE features. In advanced melanoma, the texture of the mole may change. The skin on the surface may break down and look scraped. It may become hard or lumpy. The surface may ooze or bleed. Sometimes the melanoma is itchy, tender, or painful.
The only way to diagnose melanoma is to remove tissue and check it for cancer cells. The doctor will remove all or part of the skin that looks abnormal. Usually, this procedure takes only a few minutes and can be done in a doctor's office, clinic, or hospital. The sample will be sent to a lab and a pathologist will look at the tissue under a microscope to check for melanoma.
Differences between a common mole, a dysplastic nevus, and a melanoma
Common moles, dysplastic nevi, and melanoma vary by size, color, shape, and surface texture. The list below summarizes some differences between moles and cancer. Another important difference is that a common mole or dysplastic nevus will not return after it is removed by a full excisional biopsy from the skin, but melanoma sometimes grows back. Also, melanoma can spread to other parts of the body.
Common Mole (Nevus)
- Is it cancer? No. Common moles rarely become cancer.
- How many people have common moles? Most Americans—about 327 million people—have common moles.
- How big are they? Usually less than 5 millimeters wide, or about 1/4 inch (not as wide as a new pencil eraser).
- What color are they? May be pink, tan, brown, black (in people with dark skin), or a color that is very close to a person’s normal skin tone. The color is usually even throughout.
- What shape are they? Usually round or oval. A common mole has a distinct edge that separates it from the rest of the skin.
- What is the surface texture? Begins as a flat, smooth spot on the skin. May become raised and form a smooth bump.
- Is it cancer? No. A dysplastic nevus is more likely than a common mole to become cancer, but most do not become cancer.
- How many people have dysplastic nevi? About 1 in 10 Americans—about 33 million people—have at least one dysplastic nevus.
- How big are they? Often wider than 5 millimeters (wider than a new pencil eraser).
- What color are they? May be a mixture of tan, brown, and red or pink shades.
- What shape are they? Have irregular or notched edges. May fade into the rest of the skin.
- What is the surface texture? May have a smooth, slightly scaly, or rough, irregular, and pebbly appearance.
Is it cancer? Yes.
How many people have melanoma? Melanoma is much less common than other kinds of skin cancer. But every year, about 2 in 10,000 Americans develop melanoma.