Skin cancer — the abnormal growth of skin cells — most often develops on skin exposed to the sun, but it also can occur on areas of skin not ordinarily exposed to sunlight. Skin cancer is the most common form of cancer in the U.S. "And the incidence of skin cancer is rising," says Dr. Dawn Davis, a Mayo Clinic dermatologist. The three major types of skin cancer are basal cell carcinoma, squamous cell carcinoma and melanoma. Early detection of skin cancer gives you the best chance for successful skin cancer treatment.