What are basal cell carcinomas?

Related conditions:
Basal cell epitheliomas

Definition:

Basal cell carcinoma is a cancer that begins in the basal cells of the epidermis, the outer layer of the skin. It is the most common type of skin cancer.

Risk factors:
Exposure to ultraviolet light is the primary risk factor. People with light skin and eyes are more susceptible because they have less melanin, the pigment that colors skin and blocks the sun’s radiation. People who are exposed to more ultraviolet light because they work outdoors or use tanning booths are also at greater risk. Children are particularly susceptible to skin damage from the sun because they burn more readily. Other types of radiation exposure, arsenic exposure (usually from contaminated drinking water), preexisting skin injuries such as burns or scars, and a weakened immune system are other risk factors.

Etiology and the disease process: Basal cell carcinomas begin in the skin's basal layer, which is the deepest layer of the epidermis. Basal cells continually divide to form new cells for skin, hair, or glands. They become cancerous when a mutation in their deoxyribonucleic acid (DNA) causes them to multiply rapidly instead of dying. The most common cause of basal cell carcinoma is ultraviolet (UV) radiation, the shorter-wavelength UVB subtype more so than the long-wavelength UVA. These rays can strike the nuclei of skin cells and damage chromosomes or DNA. The body repairs most of the damage to the chromosomes, but cells that are not repaired can begin to divide wildly and become cancer cells, which destroy surrounding cells or tissues. Basal cell carcinomas are slow growing and rarely spread to other parts of the body. If left untreated, however, they can do extensive damage to surrounding tissue.

Incidence: Basal cell carcinoma is the most common skin cancer, accounting for approximately 80 percent of all skin cancers, according to the American Cancer Society, with an estimated 2.8 million cases diagnosed in the United States each year. About 90 percent of those are attributed to solar radiation, although some cases occur in skin rarely exposed to the sun. Men have historically been at higher risk than women, probably because they have worked outdoors more in the past; over time, this disparity has gradually lessened. Basal cell carcinoma is more common in adults than in children, and the elderly are the most likely candidates, as these cancers can take twenty to fifty years to manifest after radiation exposure.

Symptoms: The most common symptom of basal cell carcinoma is a skin lesion, which is a superficial growth or a sore that does not heal. There are many types of basal cell carcinoma and nearly as many types of lesions. Lesion size varies from a few millimeters to several centimeters, and some lesions are larger than they appear on the skin because they invade underlying tissues. The lesions are usually painless, though the surrounding skin can become irritated and tender. Some lesions are flat, reddish or crusty patches that can be mistaken for psoriasis or eczema. The color and appearance of lesions varies widely, from white or yellow and scarlike to pink, red, tan, brown, or black. Lesions are often waxy or translucent in appearance, and many are described as pearly. Some lesions are smooth and symmetrical, while others have irregular borders or a bumpy surface with superficial blood vessels. Other lesions have rolled edges with a crater in the middle. Many lesions bleed easily.

Screening and diagnosis: Health-care providers look for skin cancers as circumstances allow or warrant. The diagnosis of basal cell carcinoma is made by histological, or microscopic, examination of lesional cells from a biopsy of the lesion. The type and variety of cancer are determined by the makeup and differentiation of cells.

Treatment and therapy: The most common treatment for basal cell carcinoma is surgical excision, or removal, of the lesion. Some normal tissue is taken all around the lesion so that the physician can be sure no cancer cells are left. Mohs surgery, which allows for better margin control, is the treatment of choice for sclerosing basal cell carcinoma. Other treatments include curettage and electrodesiccation, in which the lesion is scraped away and any remaining cancerous cells are destroyed with electric current; cryosurgery, in which the cancerous cells are frozen with liquid nitrogen; topical treatment with a drug such as imiquimod or 5-fluorouracil; radiation; laser surgery, in the case of a superficial carcinoma on the skin's surface; and photodynamic therapy, in the case of multiple carcinomas, in which a photosensitizing chemical is absorbed into the lesion, which is then exposed to a laser beam.

Prognosis, prevention, and outcomes: According to the National Cancer Institute, between 85 and 99 percent of primary tumors never recur following treatment. One variant of basal cell carcinoma, called sclerosing or morpheaform, is more likely to recur after treatment. This variant, which is classified as an infiltrative carcinoma and usually resembles a scar, is more difficult to treat because it grows in thin strands that may be missed in the tissue sample. Though death from basal cell carcinoma is extremely rare, untreated lesions can cause extensive damage and disfigurement, sometimes requiring skin grafts or reconstructive surgery. Early detection and treatment give the best outcomes. Basal cell carcinoma is also highly preventable through avoidance of excessive sun exposure, particularly in childhood. Childhood exposure to ultraviolet radiation can result in skin cancer that appears decades later. Limiting sun exposure, using sunscreen, and wearing sun-protective clothing and hats are useful methods of preventing damage to the skin from ultraviolet light.

Burns, Carrine A., and Marc D. Brown. “Imiquimod for the Treatment of Skin Cancer.” Dermatology Clinics 23.1 (2005): 151–64. Print.

Firnhaber, Jonathon M. "Diagnosis and Treatment of Basal Cell and Squamous Cell Carcinoma." American Family Physician 86.2 (2012): 161–68. Print.

Kraft, Stefan, and Scott R. Granter. "Molecular Pathology of Skin Neoplasms of the Head and Neck." Archives of Pathology & Laboratory Medicine 138.6 (2014): 759–87. Print.

Marks, James G., Jr., and Jeffrey J. Miller. Lookingbill & Marks' Principles of Dermatology. 5th ed. Philadelphia: Saunders, 2013. Print.

Neale, Rachel E., et al. “Basal Cell Carcinoma on the Trunk Is Associated with Excessive Sun Exposure.” Journal of the American Academy of Dermatology 56.3 (2007): 380–86. Print.

Noble, John, et al, eds. Textbook of Primary Care Medicine. 3rd ed. St. Louis: Mosby, 2001. Print.

Rapini, Ronald P. Practical Dermatopathology. 2nd ed. Philadelphia: Saunders, 2012. Print.

"Skin Cancer: Basal and Squamous Cell." American Cancer Society. Amer. Cancer Soc., 20 Feb. 2014. Web. 5 Sept. 2014.