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What is Skin Cancer?

Skin Cancer Types, Causes, Symptoms, and Treatment

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Updated June 14, 2014

Squamous cell carcinoma

Squamous cell carcinoma

Photo © A.D.A.M.

What is Cancer?

Normal cells in your body divide in an orderly and balanced fashion. Cancer occurs when certain cells begin to grow out of control. Cancer cells can also spread to other parts of the body through the blood, nerves or lymph system, in a process called metastasis.

What is Skin Cancer?

Skin cancer is a cancer of the cells in the outermost layer of skin, called the epidermis. The epidermis itself has three layers: an upper and middle layer made up of squamous cells, and a bottom layer made up of melanocytes and basal cells. Different types of skin cancer affect each of these types of cells, including the following most common forms:

Basal Cell Carcinoma
Basal cell carcinoma (BCC) is the most common form of skin cancer, accounting for 75% to 80% of cases. Upwards of one million people are diagnosed with basal cell carcinoma each year in the United States. It was once found mostly in middle-aged or older people but now it is also being seen at younger ages. Basal cell carcinoma usually begins on areas exposed to the sun such as the head and neck. It is a slow-growing cancer that rarely spreads to other parts of the body, but people with a history of BCC are at higher risk for getting a second BCC. If basal cell carcinoma is not treated, it can damage the surrounding tissue, including bone. Treatments are very effective, however, if the tumor is detected while it is small and thin.

Squamous Cell Carcinoma
Squamous cell carcinoma (SCC) accounts for 16% to 20% of skin cancer cases and occurs twice as often in men than in women. Approximately 200,000 to 300,000 people are diagnosed with squamous cell carcinoma each year in the United States, and about 2,500 die from the disease. It usually appears on the face, ear, neck, lips, and backs of the hands. SCC can also begin within scars or skin ulcers on other places on the body. As with basal cell carcinoma, the available treatments are very effective if the tumor is detected while it is small and thin.

Melanoma
Melanoma affects cells called melanocytes, which produce the skin's color. Melanoma can appear in an area no different from surrounding skin, or it can develop from or near a mole. It is found most frequently on the backs of both men and women or on the legs of women, but melanoma can occur anywhere on the body, including the head and neck, soles of the feet, fingernails, and other areas not exposed to the sun. Melanoma is much more dangerous than the other types of skin cancer: 62,000 people will be diagnosed with melanoma in the United States in 2008 and over 8,400 will die from the disease. Unfortunately, it is increasing at a faster rate than for any other cancer, with the exception of lung cancer in women. In the United States, the incidence of malignant melanoma from 1973 to 2002 increased by 270%. Melanoma is treatable in its early stages, but survival drops precipitously when it metastasizes to distant lymph nodes or organs.

What Causes Skin Cancer?

Besides lung cancer, skin cancer is one of the most preventable types of cancer. This is due to the fact that the major risk factor is ultraviolet (UV) radiation. The sun is, of course, the main source of UV radiation, but it can also come from tanning booths. The amount of UV exposure depends on the strength of the light, how long the skin was exposed, and whether the skin was covered with clothing or sunscreen. Many studies also show that being sunburned at a young age increases the likelihood of skin cancer even decades later.

The other major risk factor is fair skin. Skin cancer is much more common in Caucasians than in African-Americans, for example. This is because the pigment, called melanin, offers some protection from UV radiation and people with dark skin have more melanin. People with fair skin that freckles or burns easily are at especially high risk. However, remember that people of all races and skin colors can get skin cancer.

Other causes of skin cancer include:

  • long-term exposure to chemicals such as arsenic, tar and oil
  • radiation from other cancer treatments
  • previous history of skin cancer
  • family history of skin cancer
  • scars from burns or previous skin infections
  • certain treatments for psoriasis involving UV light
  • certain rare skin diseases, such as xeroderma pigmentosum and basal cell nevus syndrome
  • weakened immune system
  • infection by certain types of human papilloma virus
  • smoking
  • certain types of moles
  • other risk factors

Each year, over one million people are diagnosed with cancer of the skin, making it the most common type of cancer in the United States. Unfortunately, it is also one of the few types of cancer that has become more common in recent years. The good news is that skin cancer is one of the most preventable and treatable of all cancers.

Sources:

"Melanoma – Treatment Guidelines for Patients." National Comprehensive Cancer Network and the American Cancer Society. 21 July 2008.

"What You Need to Know about Skin Cancer." National Cancer Institute. July 2002. 21 July 2008.

"All About Skin Cancer – Melanoma." American Cancer Society. July 2008. 22 July 2008.

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