Squamous cells: Thin, flat cells that form the top layer of the epidermis.
Basal cells: Round cells under the squamous cells.
Melanocytes: Cells that make melanin and are found in the lower part of the epidermis. Melanin is the pigment that gives skin its natural color. When skin is exposed to the sun, melanocytes make more pigment and cause the skin to darken.
Skin cancer can occur anywhere on the body, but it is most common in skin that is often exposed to sunlight, such as the face, neck, hands, and arms.
The most common types are basal cell carcinoma and squamous cell carcinoma, which are nonmelanoma skin cancers. Nonmelanoma skin cancers rarely spread to other parts of the body. Melanoma is the rarest form of skin cancer. It is more likely to invade nearby tissues and spread to other parts of the body. Actinic keratosis is a skin condition that sometimes becomes squamous cell carcinoma.
This summary is about nonmelanoma skin cancer and actinic keratosis. See the following PDQ summaries for information on melanoma and other kinds of cancer that affect the skin:
- Melanoma Treatment
- Mycosis Fungoides and the Sézary Syndrome Treatment
- Kaposi Sarcoma Treatment
- Merkel Cell Carcinoma Treatment
- Unusual Cancers of Childhood Treatment
- Genetics of Skin Cancer