Skin cancer begins in the epidermis, or outer layer of skin. The epidermis is very thin, averaging only 0.2 mm (about one hundredth of an inch). It protects the deeper layers of the skin and the organs of the body from the environment. The epidermis is made up of flat cells called squamous cells. These cells form an important protein called keratin, which contributes to the skin’s ability to protect the rest of the body.
Types of Skin Cancer
The three most common types of skin cancer are melanoma, basal cell carcinoma and squamous cell carcinoma. Basal cell carcinoma and squamous cell carcinoma, along with several rare forms of skin cancer, are referred to collectively as nonmelanoma skin cancer.
Melanoma skin cancer begins in the melanocytes, the cells that produce the skin coloring or pigment known as melanin. Other names for this cancer include malignant melanoma, melanoma skin cancer and cutaneous melanoma. Melanoma is much less common than nonmelanoma, but it is much more serious and more likely to spread to other parts of the body.
Melanoma most often appears on the trunk of fair-skinned men and on the lower legs of fair-skinned women. However, people with other skin types and other areas of the skin are commonly affected. Because most melanoma cells still produce melanin, melanoma tumors are often brown or black. Although it is rare, melanomas can form in parts of the body not covered by skin such as the eyes, mouth, vagina, large intestine and other internal organs.
Basal and squamous cell carcinomas are the most common types of nonmelanoma skin cancer. They are called nonmelanoma because they develop from skin cells other than melanocytes. The two most common types of nonmelanoma include:
Basal cell carcinoma–This is a slow-growing cancer that seldom spreads to other parts of the body. It looks like a pearly growth, sometimes with an area that won’t heal. It can be translucent and grow gradually, or it can look like a sore that won’t heal.
Squamous cell carcinoma–This form of nonmelanoma also rarely spreads, but it spreads more often than basal cell carcinoma. It looks like a crusty, scaly patch with a hard, callous-like surface.
Other nonmelanoma skin cancers include Kaposi’s sarcoma, cutaneous lymphoma, skin adnexal tumors, various types of sarcomas (cancers that develop from connective tissue cells of the dermis or subcutis), and Merkel cell carcinoma. Together, these types account for less than one percent of nonmelanoma skin cancers.