What Is Skin Cancer?
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 of the skin.
- 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.
Nonmelanoma skin cancer is the most common cancer in the United States.
There are two main types of skin cancer:
- Nonmelanoma skin cancer.
- Basal cell carcinoma.
- Squamous cell carcinoma (SCC).
- Melanoma.
Basal cell carcinoma and squamous cell carcinoma of the skin, also called nonmelanoma skin cancer, 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.
In the United States, about 3 million cases of nonmelanoma skin cancer are diagnosed each year, and rates have likely been increasing in recent years. The number of cases of melanoma has been increasing for at least 40 years. Part of the reason for these increases may be that people have become more aware of skin cancer. They are more likely to have screening exams and do self-exams. As a result, they are more likely to be diagnosed with skin cancer.
From 2014 to 2018, the number of deaths from melanoma decreased slightly in all age groups.
The number of cases of childhood melanoma diagnosed in the United States is low, but increasing over time. The number of childhood deaths from melanoma has stayed about the same.
Different factors increase or decrease the risk of skin cancer.
Anything that increases your chance of getting a diseaseis called a risk factor. Anything that decreases your chance of getting a disease is called a protective factor.
Source: Skin Cancer Screening (PDQ®)–Patient Version - National Cancer Institute