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.

Moles — the medical term is "nevi" — are clusters of pigmented cells. 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. Moles may change in appearance over time — and 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.

What to look for
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. To detect melanomas or other skin cancers, use the A-B-C-D skin self-examination guide, adapted from 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 new growth in a mole larger than about 1/4 inch (6 millimeters).

What else to watch for
Other suspicious changes in a mole may include:

• Scaliness
• Itching
• 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 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.

Hidden melanomas
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. Hidden melanomas include:

• Subungual melanoma. This rare form of melanoma 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.
• Mucosal melanoma. This relatively uncommon type of 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 usually results 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.
• Ocular melanoma. 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 eyelids (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.

Common types of melanomas
Most melanomas occur in more conspicuous places. The most common melanomas include:

• Superficial spreading melanoma (SSM). Most melanomas are of this type. An SSM usually first appears as a flat or slightly raised mark that's multicolored and has an irregular border. It occurs most often on the legs in women and on the back and upper arms in men. Initially, an SSM spreads through the top layer of skin (epidermis). If it's not caught and treated at this stage, it eventually begins to grow into the underlying layers of skin — the dermis and fatty layer — and may then spread (metastasize) to other parts of your body.
• Nodular melanoma (NM). The most aggressive of all melanomas, NM usually appears as a small, round bump (nodule) with a smooth border. Most NMs are black, although some may be brown, blue, gray or even red in color. Because this type of cancer spreads so rapidly, it's often advanced by the time it's diagnosed.
• Acral-lentiginous melanoma (ALM). The most common skin cancer in people with deeper skin color, such as blacks and Asians, ALM usually develops on the palms, soles or nails. It's normally brown or black with irregular borders. Because ALM is often mistaken for a minor problem, such as a bruise or blister, it can penetrate deep into the underlying layers of skin before it's diagnosed.
• Lentigo maligna melanoma (LMM). The least threatening form of melanoma, LMM tends to develop on the nose or cheeks of older adults. Of all melanomas, LMM is most closely associated with long-term sun exposure. The lesions are flat and range in size from 0.25 to 2.4 inches (0.6 to 6 centimeters) or more. They tend to be tan, brown or black and generally don't spread to other parts of the body, but they're likely to spread in the epidermis for months or even years before spreading to the deeper layers of skin.

Sometimes people mistake seborrheic keratoses for skin cancer. Seborrheic keratoses are waxy yellow, brown or black growths that look as if they've been pasted on your skin. What causes them is unknown, but they tend to be numerous and occur commonly in people over age 40. The growths are never cancerous, but they can closely mimic a skin cancer. You may want them removed if they become irritated by clothing or for cosmetic reasons.

Although it's common to think of skin in cosmetic terms — how soft, smooth or resilient it is — your skin is your body's largest organ and performs a number of essential functions, including regulating your body temperature and protecting your body's other organs from ultraviolet radiation, injury and infection.

Your skin consists of three layers — the epidermis, dermis and subcutis. The epidermis, the topmost layer, is as thin as a pencil line. It provides a protective layer of skin cells that your body continually sheds. Squamous cells lie just below the outer surface. Basal cells, which produce new skin cells, are at the bottom of the epidermis. The epidermis also contains cells called melanocytes, which produce melanin — the pigment that gives skin its normal color. When you're in the sun, these cells produce more melanin, which helps protect the deeper layers of skin. The extra melanin is what produces the darker color of a tan. The ability to produce melanin and the way it's distributed in the skin is genetically determined; people who sunburn easily simply form less pigment than do those who tan well.

Normally, skin cells within the epidermis develop in a controlled and orderly way. In general, healthy new cells push older cells toward the skin's surface, where they die and eventually are sloughed off. This process is controlled by DNA — the genetic material that contains the instructions for every chemical process in your body. But when DNA is damaged, changes occur in these instructions. One result is that new cells may begin to grow out of control and eventually form a mass of malignant cells. How well the body repairs DNA damage is genetically determined, but it also can be affected by certain medical conditions.

Just what damages DNA in skin cells and how this leads to melanoma is a matter of intense study. Cancer is a complex disease that often results from a combination of factors rather than from a single cause. Still, excessive exposure to ultraviolet (UV) radiation is a leading factor in the development of melanoma, whether the radiation is from the sun or from tanning lamps and beds.

UV radiation and skin cancer
UV radiation is a wavelength of sunlight in a range too short for the human eye to see. Commercial tanning lamps and tanning beds also produce UV radiation. UV light is divided into three wavelength bands — ultraviolet A (UVA), ultraviolet B (UVB) and ultraviolet C (UVC). Only UVA and UVB rays reach the earth — UVC radiation is completely absorbed by atmospheric ozone, a naturally occurring substance that filters UV radiation.

At one time scientists believed that only UVB rays played a role in the development of melanoma. And UVB light does cause harmful changes in skin cell DNA, including the development of oncogenes — a type of gene that can turn a normal cell into a malignant one. But UVA light may damage melanocytes. Tanning lamps and beds mainly produce UVA radiation.

UV radiation is most intense at the equator and at high elevations, but no matter where you live, your skin absorbs UV radiation whenever you're outdoors unless you wear protective clothing and sunscreen.What's more, exposure to occasional periods of intense sunlight puts you at risk of melanoma even more than does spending long hours in the sun. An initial high dose of UV radiation will severely damage melanocytes, but not destroy them. When these damaged cells are subjected to further intense bouts of UVA light, they have little capacity to repair their DNA and so are more likely to become malignant.

Other factors in melanoma
Chronic sun exposure doesn't explain all melanomas, and recent studies suggest that sun-induced melanomas may not be as aggressive as melanomas from other causes. Other factors that may lead to melanoma include:

• Heredity. A small percentage of people who develop melanoma have a family history of the disease. Having a parent, child or sibling with melanoma greatly increases your risk. In addition, some families are affected by a condition called familial atypical multiple mole melanoma (FAMMM) syndrome. The hallmarks of FAMMM include a history of melanoma in one or more close relatives and having more than 50 moles, some of which are atypical. People with this syndrome have an extremely high risk of developing melanoma over their lifetimes. For that reason, screening for signs of skin cancer is crucial. If members of your family have FAMMM, check with your doctor about getting a screening exam every four to six months.
• Age. In general, the risk of developing melanoma increases with age. About half of adults with melanoma receive their initial diagnoses when they're in their 50s. But younger people also can develop skin cancer. In fact, melanoma is one of the most common cancers in people under 30, according to the American Cancer Society. Complicating matters further, the age at which melanomas tend to develop appears to be different for men and women. In general, women have a higher rate of melanoma than men do until age 40. After age 40, the rate for men rises dramatically. Researchers don't yet know the reason for the disparity, although they believe hormonal factors may play a role. After age 60, the melanoma rate for women increases. Overall, however, men have a greater lifetime risk of melanoma than women do.
• Carcinogens. The American Cancer Society has identified several substances that may contribute to melanoma, including coal tar, the wood preservative creosote, arsenic compounds in pesticides and radium.

As with other types of cancer, it's likely that many melanomas result from a combination of environmental and genetic factors.

Factors that may increase your risk of skin cancer include:

• Fair skin. Having less pigment (melanin) in your skin means you have less protection from damaging UV radiation. If you have blond or red hair, light-colored eyes and you freckle or sunburn easily, you're more likely to develop melanoma than is someone with a darker complexion. Fair-skinned people of Northern European ancestry are particularly at risk. Queensland, Australia, has the highest skin cancer rate in the world because it has unusually high levels of UV radiation and because most of its inhabitants are of English or Irish descent.

  Though less common, melanoma can develop in people with darker complexions, including Hispanics and blacks. For these people, melanoma is often diagnosed in the later stages, when the lesions are deeper and more advanced. Survival from melanoma is related almost entirely to the depth of invasion at the time of diagnosis. So it's important that people of all ethnic backgrounds be aware of melanoma and take precautions against UV radiation.

• A history of sunburn. Every time you burn your skin, you increase your risk of developing skin cancer. People who have had one or more severe, blistering sunburns as a child or teenager are at increased risk of skin cancer as an adult. For that reason, it's particularly important to protect children from the sun, not just with sunscreen but also with a hat, protective clothing and dark glasses. Although sunburns in adulthood also are a risk factor, the greatest damage seems to occur before you're 18. Infants are particularly vulnerable because the melanin in their skin isn't yet fully developed.
• Excessive sun exposure. Exposure to UV radiation is the leading cause of all skin cancers, including melanoma.
• Sunny or high-altitude climates. Living in a sunny climate exposes you to more UV radiation than does living in a cool, cloudy climate. In the United States, skin cancer is far more common in Arizona than in Minnesota. If you live at a high elevation, where the sun is stronger, you're also exposed to more UV radiation.
• Moles. Having just one dysplastic mole doubles your risk of melanoma. But it's not only atypical moles that make you more susceptible to melanoma — having more than 50 ordinary moles also increases your risk.
• A family or personal history of skin cancer. If a close relative, such as a parent, child or sibling, has had melanoma, you have a greater chance of developing it too. And if you've had melanoma once, you're more likely to develop it again.
• Weakened immune system. People with weakened immune systems are at greater risk of many diseases, including skin cancer. This includes people who have chronic leukemias, other cancers or HIV/AIDS, and those who have undergone organ transplants or who are taking medications that suppress the immune system.
• Exposure to environmental hazards. Exposure to environmental chemicals, including some herbicides, increases your risk of melanoma.
• Rare genetic disorder. People with xeroderma pigmentosum, which causes an extreme sensitivity to sunlight, have a greatly increased risk of developing melanoma because they have little or no ability to repair damage to the skin from ultraviolet light.

The American Cancer Society (ACS) recommends skin exams every three years for adults between ages 20 and 40 and yearly exams after age 40. These screening exams involve a head-to-toe inspection of your skin by someone qualified to diagnose skin cancer, such as a dermatologist or nurse specialist. If you have risk factors for skin cancer — fair skin, a history of severe sunburns, one or more dysplastic moles, or a family history of melanoma — talk to your doctor about more frequent screenings. Sometimes frequent screenings are recommended for all close family members of a person with melanoma.

In addition, the ACS recommends monthly self-exams for everyone older than 18. This helps you learn the moles, freckles and other skin marks that are normal for you, so you can notice any unusual changes. It's best to do this standing in front of a full-length mirror while using a hand-held mirror to inspect hard-to-see areas. Be sure to check the fronts, backs and sides of your arms and legs; your groin, scalp and fingernails; and your soles and the spaces between your toes.

If you notice a new skin growth, a change in an existing mole or a sore that doesn't heal in two weeks, see your doctor. Sometimes cancer can be detected simply by looking at your skin, but the only way to accurately diagnose melanoma is with a biopsy. In this procedure, your doctor or dermatologist removes all or part of the suspicious mole or growth, and a pathologist analyzes the sample.

If the mole is small, your doctor is likely to perform an excisional biopsy — such as a punch biopsy or an elliptical excision. In this procedure, the entire mole or growth is removed, along with a small border of normal-appearing skin. An incisional biopsy is more likely to be used for large moles, or for those on your hands or face, where scars are more obvious. In that case, only the most irregular part of a mole or growth is taken for laboratory analysis. Contrary to common belief, incisional biopsies don't cause melanoma to spread.

Staging
If you receive a diagnosis of melanoma, the next step is to determine the extent, or stage, of the cancer. Melanoma is staged using these criteria:

• Thickness and depth. A pathologist determines the thickness and depth of a melanoma by carefully examining it under a microscope. The thickness of a cancerous lesion is the most important factor in deciding on a treatment plan. In general, the thicker the tumor, the more serious the disease.
• Spread. It's also important to determine whether melanoma cells have spread to the lymph nodes. To do so, your surgeon may use a procedure known as a sentinel node biopsy. Until recently, surgeons would remove as many lymph nodes as possible to verify that the nodes didn't contain cancer cells. But this greatly increased the risk of lymphedema — severe swelling of the involved area — and other side effects. That's why a new procedure was developed that focuses on finding the sentinel nodes — the first nodes to receive the drainage from malignant tumors and therefore the first to develop cancer. If a sentinel node is removed, examined and found to be healthy, the chance of finding cancer in any of the remaining nodes is very small and no other nodes need to be removed.

Melanoma is staged using the numbers 0 through IV:

• Stage 0. This melanoma is also called in situ melanoma. At this stage, the cancer is confined to the epidermis and hasn't begun to spread. Finding and treating a cancerous tumor at this stage offers the best chance for a full recovery.
• Stages I through IV. These cancers are invasive tumors that have the ability to spread to other areas. A stage I cancer is small and well localized and has a very successful treatment rate. But the higher the stage number, the lower the chances of a full recovery. By stage IV, the cancer has spread beyond your skin to other organs, such as your lungs, liver and bone. Although it may not be possible to eliminate the cancer at this stage, treatment with radiation or biological or experimental therapies may help alleviate signs and symptoms.

The best treatment depends on your stage of cancer and your age, overall health and personal preferences. Typically, melanomas that haven't spread beyond the skin are surgically removed.

When melanoma has spread to another part of the body, options may include surgery, chemotherapy, radiation therapy, biological therapy, experimental therapy or a combination. It's important to understand the different treatments and their potential risks and side effects. Don't be afraid to discuss any questions you may have with your treatment team. You may also want to consider seeking a second opinion, especially from doctors who specialize in treating melanoma. In some cases, after weighing your options you may choose not to treat the melanoma itself but rather to try to relieve any symptoms the cancer may cause.

Treating early-stage melanomas
The best treatment for early-stage melanomas is surgical removal (simple excision). Very thin melanomas may have been entirely removed during the biopsy and require no further treatment. Otherwise, your surgeon will excise the cancer as well as a small border of normal skin and a layer of tissue beneath the skin. In almost every case this eliminates the cancer.

At one time, surgery for more invasive early-stage tumors involved cutting out the cancer along with a large border of normal skin (wide local excision). This usually meant having a skin graft — a procedure in which skin from another part of the body is used to replace the skin that's removed. But taking smaller amounts of normal skin in some cases of invasive melanomas may be just as effective in treating cancer and may eliminate the need for skin grafts.

Treating melanomas that have spread beyond the skin

• Surgical removal. It's very difficult to cure melanomas that have spread beyond the skin. But surgically removing a melanoma that has spread (metastatic melanoma) can often provide relief of symptoms — sometimes for years. Whether this is an option for you will depend on where the cancer is located and how severe it is, as well as on your own wishes and overall health.
• Chemotherapy. This form of treatment uses drugs to destroy cancer cells. Two or more drugs are often given in combination and may be administered intravenously, in pill form or both — usually for four to six months. Melanoma has long been thought to be resistant to most forms of chemotherapy, but new chemotherapy regimens are being studied and developed. In the meantime, chemotherapy is sometimes used to relieve symptoms in people with advanced metastatic melanoma.
• Radiation therapy. This treatment uses high-energy X-rays to kill cancer cells. It's sometimes used to help relieve symptoms of melanoma that has spread to another organ. Fatigue is a common side effect of radiation therapy, but your energy usually returns once the treatment is completed.
• Biological therapy (immunotherapy). This form of treatment is designed to help your immune system fight disease. It involves the use of biologic response modifiers (BRMs) — substances your body normally produces in response to infection. BRMs such as interleukin-2 and interferon are now produced in laboratories for use in treating cancer and other diseases. Side effects include signs and symptoms similar to those of the flu, such as chills, fever, nausea, vomiting and diarrhea, but they're often extremely severe. Researchers are investigating new forms of immunotherapy that not only are more effective but also cause fewer side effects. Scientists have a particular interest in vaccines that stimulate cellular immunity. The vaccines, which are made from proteins extracted from cancer cells and given in a series of injections over a period of years, are now being studied in clinical trials.
• Gene therapy. An area of great interest among researchers, this therapy generally focuses on adding genes to cancer cells. One approach, which has had limited success, is to replace some of the damaged genes that seem to be responsible for abnormal cell growth. Researchers have also tried adding a gene to melanoma cells in an effort to make the cells sensitive to drugs that normally don't affect cancer. A third strategy is to add genes to certain cancer cells, which are then used to produce a vaccine. This approach is highly experimental, however, and has not yet proved effective.

The best news about melanoma is that many cases of skin cancer can be prevented simply by following these precautions:

• Avoid the sun between 10 a.m. and 4 p.m. Because the sun's rays are strongest during this period, try to schedule outdoor activities for other times of the day, even in winter or when the sky is cloudy. You absorb UV radiation year-round, and clouds offer little protection from damaging rays.

• Wear sunscreen year-round. Sunscreens don't filter out all harmful UV radiation, especially the radiation that can lead to melanoma. But they play a major role in an overall sun-protection program. Be sure to use a broad-spectrum sunscreen with a sun protection factor (SPF) of at least 15 when you go outside, year-round. Use a generous amount of sunscreen on all exposed skin, including your lips, the tips of your ears, and the backs of your hands and neck.

  For the most protection, apply sunscreen 20 to 30 minutes before sun exposure and reapply it every two hours throughout the day, as well as after swimming or exercising. Apply sunscreen to young children before they go outdoors, and teach older children and teens how to use sunscreen to protect themselves. Keep a bottle of sunscreen in your car as well as with your gardening tools and sports and camping gear to remind yourself and your family to use it.

  In July 2006, the Food and Drug Administration (FDA) approved a new over-the-counter sunscreen that will be marketed in the United States as Anthelios SX. The new sunscreen offers better protection from UVA rays than do traditional broad-spectrum sunscreens, according to the manufacturer. This may help reduce the risk of various types of skin cancer — including melanoma and basal and squamous cell carcinomas. Better UVA protection also may reduce sun-related skin wrinkling. But the added protection may come at a cost. Although U.S. prices aren't yet available, similar products sold in Canada cost about twice as much as traditional sunscreens — or even more.

• Wear protective clothing. Sunscreens don't provide complete protection from UV rays. That's why it's a good idea to also wear dark, tightly woven clothing that covers your arms and legs, and a broad-brimmed hat, which provides more protection than a baseball cap or visor does. Some companies also sell photoprotective clothing. Your dermatologist can recommend an appropriate brand. Don't forget sunglasses. Look for those that block both UVA and UVB rays.
• Avoid tanning beds and tan-accelerating agents. Tanning beds emit UVA rays, which may be as dangerous as UVB rays — especially since UVA light penetrates deeper into your skin and causes precancerous skin lesions.
• Be aware of sun-sensitizing medications. Some common prescription and over-the-counter drugs — including antibiotics; certain cholesterol, high blood pressure and diabetes medications; birth control pills; nonsteroidal anti-inflammatories such as ibuprofen (Advil, Motrin, others); and the acne medicine isotretinoin (Accutane) — can make your skin more sensitive to sunlight. Ask your doctor or pharmacist about the side effects of any medications you take. If they increase your sensitivity to sunlight, be sure to take extra precautions.
• Check your skin regularly and report changes to your doctor. Examine your skin often for new skin growths or changes in existing moles, freckles, bumps and birthmarks. With the help of mirrors, check your face, neck, ears and scalp. Examine your chest and trunk, and the tops and undersides of your arms and hands. Examine both the front and back of your legs, and your feet, including the soles and the spaces between your toes. Also check your genital area, including between your buttocks.
• Have regular skin exams. Consult your doctor for a complete skin exam every year if you're older than 40, or more often if you're at high risk of developing melanoma.