Skin cancer is a disease in which malignant (cancer) cells form in the tissues of the skin.
The skin is the body's largest organ. It protects against heat, sunlight, injury, and infection. Skin also helps control body temperature and stores water, fat, and vitamin D. The skin has several layers, but the two main layers are the epidermis (top or outer layer) and the dermis (lower or inner layer). Skin cancer begins in the epidermis, which is made up of three kinds of cells:
- Squamous cells: Thin, flat cells that form the top layer of the epidermis. Cancer that forms in squamous cells is called squamous cell carcinoma.
- Basal cells: Round cells under the squamous cells. Cancer that forms in basal cells is called basal cell carcinoma.
- Melanocytes: Found in the lower part of the epidermis, these cells make melanin, the pigment that gives skin its natural color. When skin is exposed to the sun, melanocytes make more pigment and cause the skin to tan, or darken. Cancer that forms in melanocytes is called melanoma.
Anatomy of the skin, showing the epidermis, dermis, and subcutaneous tissue.
Nonmelanoma skin cancer is the most common cancer in the United States.
Basal cell carcinoma and squamous cell carcinoma are also called nonmelanoma skin cancer and are the most common forms of skin cancer. Most basal cell and squamous cell skin cancers can be cured.
Melanoma is more likely to spread to nearby tissues and other parts of the body and can be harder to cure. Melanoma is easier to cure if the tumor is found before it spreads to the dermis (inner layer of skin). Melanoma is less likely to cause death when it is found and treated early.
Anatomy of the skin, showing the epidermis, dermis, and subcutaneous tissue. Melanocytes are in the layer of basal cells at the deepest part of the epidermis.
In the United States, the number of cases of nonmelanoma skin cancer seems to have increased in recent years. The number of cases of melanoma has increased over the last 30 years. Part of the reason for these increases may be that people are more aware of skin cancer. They are more likely to have skin exams and biopsies and to be diagnosed with skin cancer.