Skin cancer is the abnormal growth of skin cells. It may first appear as a new mole, a change in a growth or mole, a sore that does not heal, or an irritation of the skin.

Exposure to the sun is the most common cause of skin cancer. Problems with the body's defense system (impaired immune system) and a family history of skin cancer also increase a person's risk.

There are 3 major types of skin cancer:

• Basal cell skin cancer is the most common form. It is a slow-growing cancer that seldom spreads to other parts of the body.
• Squamous cell skin cancer is less common than the basal cell form. It also rarely spreads, especially if it is found and treated early. But squamous cell skin cancer is more likely to spread than basal cell carcinoma.
• Melanoma grows and spreads rapidly and can invade other organs, such as the liver, lungs, or brain. Melanoma can develop in an existing mole or other mark on the skin, but it may form in unmarked skin.

Skin cancer is treated by removing the cancerous area with either surgery (excision) or freezing (cryotherapy). For melanomas that have spread to the lymph nodes, other treatments may be used after surgery.