Melanoma is a disease in which malignant (cancer) cells form in the skin. Skin cancer is the most common cancer, and is increasing rapidly. Although more benign forms of skin cancer such as basal cell and squamous cell carcinomas are on the rise, the greatest increase has been in melanoma, the most serious and most deadly type of skin cancer. In fact, the percentage of people with melanoma has more than doubled in the last 30 years.

Melanoma develops in the cells that produce melanin (melanocytes) - the pigment that gives your skin its color. It can also form in your eye (intraocular melanoma) and in rare cases in internal organs such as your intestine. But most melanomas develop in your skin.

Although they make up the smallest percentage of all skin cancers, melanomas cause the greatest number of deaths. That's because they're more likely than other skin cancers to spread to different parts of your body (metastasize). 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 the disease.

Avoiding excessive sun exposure can prevent many melanomas. And knowing the warning signs of skin cancer can help ensure that malignant changes are detected and treated before they can spread. Melanoma can be successfully treated if it's caught early.

Signs and symptoms

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 average about one-quarter 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 they may change in appearance over time and some may even disappear as you grow older.

Sometimes you may have one or more large (more than one-half 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 malignant than normal moles are.

In fact, the first sign of melanoma is often a change in an existing mole or the development of a new, unusual-looking growth on your skin. The American Academy of Dermatology has developed an ABCD guide for determining when a mole is a matter for concern:

• A is for asymmetry. Symmetrical round or oval growths are usually noncancerous (benign). Be alert for irregular shapes, where one half is different from the other.

• B is for border. Have your doctor check moles with notched, scalloped or vaguely defined borders.

• C is for color. Look for growths that have many colors or an uneven distribution of color. Growths that have the same overall color are usually benign.

• D is for diameter. Consult your doctor if you have any growths that are larger than one-quarter inch (6 millimeters) — about the diameter of a pencil eraser.

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

Cancerous (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. They can also develop on almost any part of your body.

Some melanomas develop on skin that's frequently exposed to the sun such as your face, lips, hands and arms. You can prevent these by wearing sunscreen and protective clothing. But the majority of melanomas occur in less exposed areas. In men they're often found on the back. Women tend to develop melanomas on their lower legs.

Melanomas can also develop in 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 your thumb or your 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 or that doesn't heal after 2 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 hard to detect because they can easily be mistaken for other, far more common conditions. A melanoma that develops in your esophagus, for instance, causes pain that's similar to a sore throat. A melanoma in a woman's genital tract usually results in itching and bleeding — symptoms associated with 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, so having regular dental checkups can help catch this type of cancer. Having regular Pap tests can help spot melanomas in the vagina.

• Ocular melanoma. Symptoms of this type of melanoma, which may develop in the lining of your eyelids (conjunctiva) or the pigmented coating within your eyeball (choroid), include a scratchy feeling under your eyelid or a dark spot in your vision. The number of white American men with conjunctival melanoma have increased greatly over the past 30 years, most likely as a result of sun exposure. This increase emphasizes the importance of wearing dark glasses when you're spending time in the sun.

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

• Superficial spreading melanoma (SSM). Approximately two-thirds of all melanomas are of this type. An SSM usually first appears as a flat or slightly raised mark that's dark with variegated colors and an irregular border. It occurs most often on the legs in women and on the back and upper arms in men. It can also occur on the soles or palms, especially in people of African or Asian descent. 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 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 quite 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 may have penetrated 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. The lesions are flat and range in size from 1.2 inches to 2.4 inches (3 centimeters to 6 centimeters) or more. They tend to be tan, brown or black and generally don't spread to other parts of the body. Instead, 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 occur in fair-skinned people older than 40. The growths aren't cancerous, but you may want them removed for cosmetic reasons.

• Skin cancer

• Yeast infection

Causes

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 protecting you from temperature extremes, 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."

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.

Just what damages DNA in skin cells and how this leads to melanoma is under 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.

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 also damage melanocytes. People who visit commercial tanning salons are especially at risk because tanning lamps and beds mainly produce UVA radiation.

Even so, UVB light remains a major concern, especially because of the ongoing depletion of atmospheric ozone, which normally screens the earth from some UVB radiation. In the past two decades, ozone levels have, primarily from widespread use of chlorofluorocarbons (CFCs) — synthetic chemicals commonly used as refrigerants, solvents and foam-blowing agents. Less ozone means that more UVB radiation reaches the ground.

Scientists are divided on just how much ozone depletion has contributed to the rise in skin cancer. They cite other factors, such as an increase in outdoor activities and sunbathing, as well as a trend toward skimpier clothing. Yet ozone depletion remains a serious concern.

In addition, the amount of UVB light reaching the earth varies considerably from one geographic region to another. Rays are strongest closer to the equator and at high altitudes.

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 greater risk of melanoma than 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.

Chronic sun exposure doesn't explain all melanomas. 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. Damage to the tumor suppressor gene, p16, appears to play a role in inherited melanomas.

• In addition, some families are affected by a condition called familial atypical multiple mole and 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. For that reason, screening for signs of skin cancer is crucial. Check with your doctor about getting a screening exam every 4 to 6 months.

• Age. In general, your risk of developing melanoma increases with age. But younger people can also develop skin cancer, and melanoma is, in fact, one of the most common cancers in people under 30. 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 once again 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 pitch used in road paving, 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.

• Skin cancer

• Yeast infection

 

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