Skin cancer is the most common human cancer, according to the American Cancer Society (ACS). Three types account for more than 99 percent of all skin cancers: basal cell carcinoma, squamous cell carcinoma and melanoma. More than 1 million new cases of skin cancer are diagnosed each year in the United States, the ACS reports. The risk of developing skin cancer is heightened by exposure to ultraviolet (UV) radiation from the sun or artificial sources.
Basal Cell Carcinoma of the Skin
Basal cell carcinoma of the skin (BCC) is the most common malignant tumor in the United States with approximately 800,000 to 900,000 new cases identified each year, the American Academy of Dermatology (AAD) reports. Eighty percent of skin cancers in the United States are BCC. The risk of BCC is inversely related to the depth of your skin color; the lighter your complexion, the greater your risk of BCC.
BCC arises when basal cells from the deepest layer of the skin become cancerous. The cancerous transformation of basal cells is usually due to damage from UV light. Hence, BCC is typically seen on sun-exposed areas such as the nose, ears, face, and neck. BCC nodules are often pink or red with a waxy appearance.
BCC can be disfiguring if left untreated, but it is generally not life-threatening.
Squamous Cell Carcinoma
Squamous cell carcinoma of the skin (SCC) is the second most common form of skin cancer. Approximately 200,000 new cases of SCC are diagnosed in the United States each year, accounting for roughly 16 percent of all skin cancers, the AAD says. Notably, according to an article in the November 2006 "Journal of the American Academy of Dermatology," SCC occurs more frequently than BCC among people of color.
SCC arises from the cancerous transformation of skin cells called keratinocytes. The most common risk factor for SCC is UV exposure. Less-common risk factors not related to sun damage include exposure to insecticides, herbicides and other chemicals, repeated heat-related injuries, and chronic immunosuppression.
SCC occurs most commonly on sun-exposed areas among Caucasians, but it can occur anywhere on the skin including mucosal surfaces. SCC typically presents as a scaly or crusty patch of skin. The base of the patch is usually red and may resemble a non-healing ulcer.
SCC can spread to other organs, a process called metastasis. The risk of metastasis ranges from 0.5 to 35 percent, depending on the site of the tumor and its characteristics. Metastatic SCC can be life-threatening.
Melanoma
Though once rare, the incidence of melanoma has risen dramatically in the United States over the past century. The American Cancer Society estimated that nearly 69,000 new cases of melanoma were diagnosed in the United States in 2009, accounting for approximately 4 percent of all skin cancers.
Melanoma arises from the cancerous transformation of cells called melanocytes. These cells normally produce melanin, the substance that gives our skin its color and helps protect against UV damage. However, exposure to both forms of UV radiation---UVA and UVB---are linked to melanoma risk. Fair skin, red or blond hair, green or blue eyes, and a family history of melanoma are associated with an increased relative risk for the disease.
The American Academy of Dermatology states that melanomas most often occur on the upper back, torso, lower legs, head and neck, although they can occur anywhere on the skin. Melanomas are best described as unusual-looking moles. They can arise in a preexisting mole, but most are believed to develop as new growths.
Melanoma can metastasize early in the course of the disease. Early detection is essential.
References
- "American Cancer Society": Cancer facts and figures 2009
- "Clinical Oncology, Third Edition"; Martin D. Abeloff, M.D., James O. Armitage, M.D., John E. Niederhuber, M.D., Michael B. Kastan, M.D., Ph.D., W. Gilles McKenna, M.D., Ph.D., Editors; 2004
- "American Academy of Dermatology": What is skin cancer?
- "Journal of the American Academy of Dermatology"; Skin cancer in skin of color; H.M. Gloster, Jr., K. Neal; November 2006
- "American Academy of Dermatology": Melanoma fact sheet
