Skin cancer is the most common type of cancer in the United States. More than 1 million cases are diagnosed each year, and according to current estimates, 40 to 50 percent of Americans will have skin cancer at least once by the time they are age 65. Basal cell carcinoma, squamous cell carcinoma, and malignant melanoma are the three most common types of skin cancer.
Basal cell carcinoma accounts for more than 90 percent of all skin cancers. Basal cell cancer grows slowly and does not usually spread to other parts of the body. However, if left untreated, it can spread to nearby areas and invade bone and other tissues under the skin.
Squamous cell carcinoma is much less common than basal cell carcinoma. It can be more aggressive than basal cell carcinoma and is also more likely to grow deep below the skin and spread to distant parts of the body. When squamous or basal cell skin cancers are found early, there is nearly a 100 percent chance for cure.
Malignant melanoma is less common than basal or squamous cell skin cancers, but it is more dangerous than either and can be deadly. If caught early, there is nearly a 97 percent chance for cure.
Actinic keratosis, or solar keratosis, is a precancerous condition that has the potential for developing into squamous cell carcinoma. It appears as rough red or brown, scaly patches on the skin. They are often more easily felt than seen. Like skin cancer, actinic keratosis is usually found on sun-exposed areas of the body, but it can be found on other parts of the body as well.
Skin cancer can be deadly, but nearly all skin cancer can be treated if it is detected and diagnosed early.
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The skin is the body's largest organ. It protects against heat, sunlight, injury, and infection. It has two main layers: the epidermis (upper or outer layer) and the dermis (lower or inner layer). Basal and squamous cell skin cancers occur most often in the epidermis. Basal cells are found in the base of the epidermis, while squamous cells form the surface.
Melanoma begins in the pigment-producing cells called melanocytes located in the junction of the epidermis and the dermis. A group of melanocyte cells form a mole, which is usually dark and may be raised from the skin. Melanocyte cells are responsible for producing melanin, the pigment that gives skin its natural color and darkens when exposed to sunlight.
Cancer begins in the body's cells, which are constantly dividing and multiplying to replace old, damaged cells. Sometimes, cells begin to divide unnecessarily, forming excess tissue known as a tumor. In most cases, tumors are benign, meaning that they are not cancerous. Benign tumors, although they may cause some health problems depending on their size and location, are not life threatening.
However, if an abnormal cell begins to divide, it eventually forms a malignant or cancerous tumor. Most malignant tumors grow quite rapidly, invading nearby organs and tissues. Cancerous cells travel through the bloodstream to other regions of the body. When cancer spreads from its original site, the process is known as metastasis.
The majority of cancers—about 80 percent—are considered sporadic, meaning no clear cause is known. But for skin cancers, the cause is usually overexposure to the sun's harmful UV rays. They cause normal genes to mutate or change, multiply rapidly, and become malignant or cancerous.
The greatest risk for developing all types of skin cancers comes from sunburns. People with fair skin and those who tend to burn easily are more at risk.
Other risk factors include:
- Age. The longer a person's skin is exposed to the sun over time, the higher the risk of developing skin cancer.
- Appearance. People who have red or blond hair, fair skin, freckles, and blue or light-colored eyes are more at risk of developing skin cancer. Skin cancer occurs less often in Hispanics, Asians, and African-Americans. However, darker-skinned people and those who tan easily can still develop skin cancer as well as suffer other long-term effects of exposure to ultraviolet light, like dry skin and premature aging.
- Climate. People who live in sunny climates are at an increased risk for skin cancer.
- Geography. People who live in southern states or in the Sun Belt are at higher risk.
- Family history. A family history of skin cancer, especially melanoma, increases the risk.
- Personal history. A person who develops skin cancer is at risk of developing the same cancer again in the same place or developing a new skin cancer somewhere else.
- Employment. Working around coal tar, arsenic compounds, creosote, pitch, and paraffin oil increases the risk of skin cancer.
- Previous injuries. Someone who has traumatized skin, such as a major scar or burn, could be at higher risk of developing skin cancer in that region.
- Actinic keratosis. A precancerous condition of thick, scaly patches of skin. Also called solar or senile keratosis. It may also appear as a cracking or peeling lower lip that does not heal with lip balm.
- Dysplastic nevi. Moles whose appearance is different from that of common moles. Dysplastic nevi are generally larger than ordinary moles and have irregular and indistinct borders. Their color frequently is not uniform and ranges from pink to dark brown; they usually are flat, but parts may be raised above the skin surface.
Last reviewed on 7/21/09
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