The glands produce sweat to help regulate body temperature and a fatty, lubricating substance called sebum to keep the skin from drying out. These substances reach the skin's surface through tiny openings called pores. Like all cancers, skin cancer is a disease of the body's cells. A skin lesion can be either benign or malignant. Benign tumors are not cancer and do not invade surrounding tissue or spread to other parts of the body.
Malignant tumors are cancer.
The most common kinds of skin cancer are basal cell carcinoma and squamous cell carcinoma. Basal cell carcinoma, which accounts for more than 90 percent of all skin cancers in the United States, is a slow-growing cancer that seldom spreads to other parts of the body. Squamous cell carcinoma spreads more frequently than basal cell carcinoma, but still it is rare. Squamous cell cancers tend to be aggressive, and often appear on sun-exposed areas of the body. Basal cell carcinoma and squamous cell carcinoma are sometimes called non-melanoma skin cancer.