Chapter 9 Skin Cancer Whos At Risk: Cancer

Content provided by the Faculty of the Harvard Medical School

Chapter 9: Skin cancer - Who's at risk

Most skin cancer develops in the epidermis, the outer layer of the skin. The most common types of skin cancer are basal cell cancer and squamous cell cancer, both of which develop in the keratinocytes, cells that produce the proteins that keep the skin healthy and resilient. These two cancers strike an estimated 1.3 million people annually. Both of these skin cancers develop after exposure to sunlight. More than four out of five basal cell cancers and at least three out of five squamous cell cancers develop on the face, neck, and head. Fortunately, these two forms of cancer rarely spread elsewhere. They are also highly curable, usually through simple surgical removal.

Malignant melanoma, although rarer, is much more deadly. This type of skin cancer develops in the melanocytes, the cells that produce melanin or skin pigment. According to the American Cancer Society, an estimated 62,480 new cases of melanoma will be diagnosed in the United States in 2008. About 8,420 people will die of this disease this year. Although malignant melanoma can be treated if it is detected early enough, it spreads quickly to other parts of the body, and once it has spread it becomes much more dangerous. In fact, malignant melanoma accounts for about four out of five skin cancer deaths annually.

The incidence of skin cancer has been increasing steadily. It is not clear why. Some experts blame the depletion of the ozone level, which normally screens out much of the sun's ultraviolet (UV) radiation. Others blame the sun-seeking culture of the United States.

Although skin cancer can run in families, most cases of skin cancer develop because of damage caused by UV radiation from the sun, which in turn damages the genetic material inside skin cells. Like the sun, tanning booths also emit damaging UV radiation. Cells may then begin to multiply and grow out of control.

Two types of UV radiation are linked to skin cancer: UV-A, which penetrates beneath the epidermis and can cause significant long-term skin damage, and UV-B, which burns the surface of the skin and is the cause of most sunburn. Both types of UV radiation can lead to changes in your skin that may eventually lead to cancer.

Some of the factors that increase your risk of skin cancer are beyond your control. These include your skin type, the number and type of moles you develop as you age, and your family history of the disease. Others, such as your sun exposure and the steps you take to protect yourself against harmful radiation, are within your control.

Three Kinds of Skin Cancer Skin cancers originate almost exclusively in the upper layer of skin, known as the epidermis, which is exposed to sunlight. Squamous Cell Cancer: Squamous cell cancers start in the middle layer of the epidermis usually affecting only the surrounding area but penetrating deeply into these tissues and gradually forming a raised patch with a rough surface. Basal Cell Cancer: Basal cell cancers originate in the lowest layer of the epidermis, the basal layer. The cells invade and destroy surrounding tissues, forming a painless bump or nodule that later becomes an open ulcer with a hard edge. Malignant Melanoma: Melanoma, the deadliest form of skin cancer, occurs when pigment-making cells in the basal layer called melanocytes begin reproducing uncontrollably, spreading to distant parts of the body.

Factors that raise your risk of skin cancer but are out of your control include:

Age. About half of all cases of melanoma occur in people over 50. But it can also strike younger people, and it is one of the most frequently occurring cancers in people under 30.

Family medical history. If either of your parents or any of your siblings or children develops melanoma, you are at increased risk yourself. Depending on the number of relatives affected, your risk can be as much as eight times that of someone who has no family history of the disease.

Skin type. White people are more than 10 times as likely to develop any type of skin cancer than are African Americans. The paler your complexion and the more prone you are to sunburn, the higher your risk. The reason has to do with the amount of melanin in your skin. When you are exposed to the sun, skin cells known as melanocytes produce more melanin to protect the skin cells from radiation. But people with lighter complexions don't produce as much melanin and so are more susceptible to radiation damage.

Moles. Some people are born with moles, which appear as dark spots on the skin. But more often, people develop moles as children or adolescents. Moles are actually small benign tumors that form when too many melanocytic cells accumulate. Although some moles do eventually turn cancerous, they are more often regarded as a sign that you are at increased risk for melanoma.

Gender. Basal cell cancers occur twice as often in men as in women; squamous cell cancers occur three times as often in men.

Last updated:	May 01, 2008