Skin cancer is the most common type of cancer in the United States. An estimated 40 to 50 percent of Americans who live to age 65 will have skin cancer at least once. Basal cell carcinoma accounts for more than 90 percent of all skin cancers in the United States. It is a slow-growing cancer that seldom spreads to other parts of the body. Squamous cell carcinoma also rarely spreads, but it does so more often than basal cell carcinoma.
Squamous cells are flat and make up most of the epidermis, the outer layer of the skin.
Basal cells are round and lie under the squamous cells. Melanoma is the most serious cancer of the skin. In some parts of the world, especially among Western countries, the number of people who develop melanoma is increasing faster than any other cancer. In the United States, for example, the number of new cases of melanoma has more than doubled in the past 20 years. If melanoma spreads to the lymph nodes, it may also reach other parts of the body such as the liver, lungs, or brain.