Basal cell carcinoma is the most common form of cancer in the US. It accounts for about 75% of all skin cancers. The incidence of skin cancer has increased greatly in recent years, due in part to greater exposure to UV radiation from the sun. In 1990, 600,000 Americans were diagnosed with either basal cell cancer or squamous cell cancer, up from 400,000 in 1980.

Basal cells are normal skin cells. They may develop cancerous changes, causing a lump or bump that is painless. A new skin growth that ulcerates, bleeds easily, or does not heal well may indicate development of basal cell skin cancer. This type of skin cancer has a high cure rate, but neglect can allow the cancer to enlarge, causing possible disability or, in rare cases, death.

More than 90% of basal cell carcinomas occur on areas of skin that are regularly exposed to sunlight or other ultraviolet radiation. They may also occur on the scalp. The onset most commonly occurs after age 40.

Other risks include a genetic predisposition -- basal cell carcinomas are more common in those who have light colored skin, blue or green eyes, blond or red hair -- and overexposure to X-rays or other forms of radiation.

This cancer usually remains local and almost never spreads to distant parts of the body, but it may continue to grow and invade nearby tissues and structures, including the nerves, bones, and brain. The tumor may begin very small, growing to 1 or 2 centimeters in diameter after several years of growth.