Basal cell carcinoma is the most common form of cancer worldwide. In the United States, it accounts for approximately 80 percent of all skin cancers. The majority of basal cell carcinomas are easily and successfully treated with current therapies.
The skin consists of three layers. The top layer, called the epidermis, is where most skin cancers, including basal cell carcinoma, arise. Below that is the dermis, the layer that contains sweat glands, oil glands, and other structures of the skin. The subcutaneous layer, which is below the dermis, is composed of fat and connective tissue and connects the skin to the underlying muscle.
Basal cell carcinomas are most commonly found on the face, neck, hands, or other parts of the body that are frequently exposed to the sun. This type of cancer can have many different appearances: a red patch or irritated area; a small, pink pearly bump; a white or yellow scar-like area; a smooth growth with a dent in the center; or an open sore that bleeds or oozes. Basal cell carcinomas rarely spread throughout the body, and deaths from this disease are very rare. However, because basal cell carcinomas often occur on the face, they can cause serious cosmetic damage and functional difficulties if not diagnosed and treated early.
Risk factors for developing basal cell carcinoma include:
Overexposure to ultraviolet (UV) radiation from the sun is the single most important cause of skin cancer, including basal cell carcinoma. UV radiation is a spectrum of invisible rays that are part of the energy produced by the sun. There are two kinds of UV radiation: UVA and UVB. UVB radiation is well known for causing sunburn, and scientists believe these rays cause most skin cancers, including basal cell carcinoma. UVA is the dominant tanning ray and, according to the National Cancer Institute, may also cause skin damage that can lead to premature aging and skin cancer.
Basal cell carcinoma is more likely to occur in people who have been exposed to intermittent bursts of UV radiation — UVB radiation, in particular — especially when the exposure results in sunburn and blistering. People who work outdoors, spend a lot of time at the beach, or regularly participate in outdoor sports have a greater risk of developing skin cancer. UVA rays can even travel through glass and clouds. Sun lamps and tanning beds are another source of exposure to harmful UVA rays and should be avoided.
People with fair skin — especially those with blond or red hair and blue or light-colored eyes — are more likely to develop skin cancer. (A propensity to freckle or sunburn can be a warning sign.) The skin of these particularly at-risk individuals contains less of the pigment melanin, which provides a degree of natural protection from the sun. People with dark skin, however, can still develop basal cell carcinoma.
People who have had skin cancer once are more likely to develop skin cancer again. As many as half of all patients diagnosed with one basal cell carcinoma develop another skin cancer within five years.
Other, less common risk factors for basal cell carcinoma include repeated exposure to radiation, and exposure to coal tar, arsenic, or other industrial compounds.
People with a weakened immune system are also at an increased risk for developing basal cell carcinoma. Examples would include certain patients with lymphoma and leukemia, on chemotherapy, or treated with drugs to prevent organ transplant rejection.
A long period of development usually occurs between exposure to harmful UV radiation and the appearance of basal cell carcinoma, putting older people at a greater risk of developing the disease. The risk also increases as people grow older because the body loses its ability to repair DNA damage over time.
Basal cell carcinomas often appear as small, smooth, shiny, or pale growths, or as a waxy lump. They also may develop from a flat area that is only slightly different in appearance from normal skin. Some basal cell carcinomas may emerge so slowly that they go unnoticed as new growths.
Basal cell carcinomas rarely cause pain in their earliest stages, although they may bleed after a minor injury and then form a scab and heal. Because this crusting and healing can recur over months or years with little apparent growth, one may mistake the tumor for a sore or wound.