Melanoma is the most serious and deadly type of skin cancer. Melanoma develops in the cells that produce melanin — the pigment that gives your skin its color. Melanoma can also form in the eyes and, rarely, in internal organs, such as the intestines.
Although melanomas make up the smallest percentage of all skin cancers, they cause the greatest number of deaths. That’s because they’re more likely to spread to different parts of the body. And the incidence of melanoma is on the rise.
The exact cause of all melanomas isn’t clear, but exposure to ultraviolet (UV) radiation from sunlight or tanning lamps and beds greatly increases the risk of developing melanoma.
Avoiding excessive sun exposure can prevent many melanomas. And knowing the warning signs of skin cancer can help ensure that cancerous changes are detected and treated before they have a chance to spread. Melanoma can be successfully treated if you catch it early.
Melanomas can develop anywhere on your body, but most often develop in areas that have had exposure to the sun, such as your back, legs, arms and face. Melanoma can occur in areas that don’t receive much sun exposure, such as the soles of your feet, palms of your hands and on fingernail beds.
The first sign of melanoma is often a change in an existing mole or the development of a new, unusual-looking growth on the skin. But melanoma can also occur on otherwise normal appearing skin.
Normal moles are generally a uniform color, such as tan, brown or black, with a distinct border separating the mole from your surrounding skin. They’re oval or round in shape and about 1/4 inch (6 millimeters) in diameter — the size of a pencil eraser.
Most people have between 10 and 40 moles. Many of these develop by age 20, although moles may change in appearance over time — some may even disappear with age. Some people may have one or more large (more than 1/2 inch, or 12 millimeters, in diameter), flat moles with irregular borders and a mixture of colors, including tan, brown, and either red or pink. Known medically as dysplastic nevi, these moles are much more likely to become cancerous (malignant) than normal moles are.
Unusual moles that may indicate melanoma
To detect melanomas or other skin cancers, use this skin self-examination guide, adapted from recommendations by the American Academy of Dermatology:
- A is for asymmetrical shape. Look for moles with irregular shapes, such as two very different-looking halves.
- B is for irregular border. Look for moles with irregular, notched or scalloped borders — the characteristics of melanomas.
- C is for changes in color. Look for growths that have many colors or an uneven distribution of color.
- D is for diameter. Look for growths that are larger than about 1/4 inch (6 millimeters).
- E is for evolving. Look for changes over time, such as a mole that grows in size or that changes color or shape. Moles may also evolve to develop new signs and symptoms, such as new itchiness or bleeding.
Other suspicious changes in a mole may include:
- Change in texture — for instance, becoming hard or lumpy
- Spreading of pigment from the mole into the surrounding skin
- Oozing or bleeding
Malignant moles vary greatly in appearance. Some may show all of the changes listed above, while others may have only one or two unusual characteristics.
Melanomas can also develop in areas of your body that have little or no exposure to the sun, such as the spaces between your toes and on your palms, soles, scalp or genitals. These are sometimes referred to as hidden melanomas because they occur in places most people wouldn’t think to check. When melanoma occurs in people of color and those with dark skin tones, it’s more likely to occur in a hidden area.
Hidden melanomas include:
- Melanoma under a nail. Subungual melanoma is a rare form of melanoma that occurs under a nail, most often on the thumb or big toe. It’s especially common in blacks and in other people with darker skin pigment. The first indication of a subungual melanoma is usually a brown or black discoloration that’s often mistaken for a bruise (hematoma). See your dermatologist if you develop a nail discoloration that increases in size, spreads to involve the cuticle or that doesn’t heal after two months.
- Melanoma in the mouth, digestive tract, urinary tract or vagina. Mucosal melanoma develops in the mucosal tissue that lines the nose, mouth, esophagus, anus, urinary tract and vagina. Mucosal melanomas are especially difficult to detect because they can easily be mistaken for other, far more common conditions. A melanoma in a woman’s genital tract may result in itching and bleeding — signs and symptoms that commonly result from a yeast infection or menstrual irregularities. And symptoms of anorectal melanoma are similar to those caused by hemorrhoids. Your dentist is trained to spot melanomas that occur in your mouth. Regular pelvic exams can help detect melanomas in the vagina.
- Melanoma in the eye. Ocular melanomas sometimes develop in the pigment-containing cells in the back portion of the eye (retina). These melanomas usually don’t produce symptoms and are only detected during eye exams. On the other hand, melanomas that occur in the lining of your eyelid (conjunctiva) or the pigmented coating within your eyeball (choroid) may cause a scratchy feeling under your eyelid or a dark spot in your vision. The best way to prevent ocular melanoma, which has been linked to chronic sun exposure, is to wear glasses rated to block 99 percent to 100 percent of ultraviolet A light when you’re in the sun.