Skin Cancer, Non-Melanoma
Skin Cancer, Non-Melanoma
Non-melanoma skin cancer is a malignant growth of the external surface or epithelial layer of the skin.
Skin cancer is the growth of abnormal cells capable of invading and destroying other associated skin cells. Skin cancer is often subdivided into either melanoma or non-melanoma. Melanoma is a dark-pigmented, usually malignant tumor arising from a skin cell capable of making the pigment melanin (a melanocyte). Non-melanoma skin cancer most often originates from the external skin surface as a squamous cell carcinoma or a basal cell carcinoma.
The cells of a cancerous growth originate from a single cell that reproduces uncontrollably, resulting in the formation of a tumor. Exposure to sunlight is documented as the main cause of almost 800,000 cases of non-melanoma skin cancer diagnosed each year in the United States. The incidence increases for those living where direct sunshine is plentiful, such as near the equator.
Basal cell carcinoma affects the skin's basal layer and has the potential to grow progressively larger in size, although it rarely spreads to distant areas (metastasizes). Basal cell carcinoma accounts for 80% of skin cancers (excluding melanoma), whereas squamous cell cancer makes up about 20%. Squamous cell carcinoma is a malignant growth of the external surface of the skin. Squamous cell cancers metastasize at a rate of 2-6%, with up to 10% of lesions affecting the ear and lip.
Causes and symptoms
Cumulative sun exposure is considered a significant risk factor for non-melanoma skin cancer. There is evidence suggesting that early, intense exposure causing blistering sunburn in childhood may also play an important role in the cause of non-melanoma skin cancer. Basal cell carcinoma most frequently affects the skin of the face, with the next most common sites being the ears, the backs of the hands, the shoulders, and the arms. It is prevalent in both sexes and most commonly occurs in people over 40.
About 1-2% of all skin cancers develop within burn scars; squamous cell carcinomas account for about 95% of these cancers, with 3% being basal cell carcinomas and the remainder malignant melanomas.
Basal cell carcinomas usually appear as small skin lesions that persist for at least three weeks. This form of non-melanomatous skin cancer looks flat and waxy, with the edges of the lesion translucent and rounded. The edges also contain small fresh blood vessels. An ulcer in the center of the lesion gives it a dimpled appearance. Basal cell carcinoma lesions vary from 4-6mm in size, but can slowly grow larger if untreated.
Squamous cell carcinoma also involves skin exposed to the sun, such as the face, ears, hands, or arms. This form of non-melanoma is also most common among people over 40. Squamous cell carcinoma presents itself as a small, scaling, raised bump on the skin with a crusting ulcer in the center, but without pain and itching.
Basal cell and squamous cell carcinomas can grow more easily when people have a suppressed immune system because they are taking immunosuppressive drugs or are exposed to radiation. Some people must take immunosuppressive drugs to prevent the rejection of a transplanted organ or because they have a disease in which the immune system attacks the body's own tissues (autoimmune illnesses); others may need radiation therapy to treat another form of cancer. Because of this, everyone taking these immunosuppressive drugs or receiving radiation treatments should undergo complete skin examination at regular intervals. If proper treatment is delayed and the tumor continues to grow, the tumor cells can spread (metastasize) to muscle, bone, nerves, and possibly the brain.
To diagnose skin cancer, doctors must carefully examine the lesion and ask the patient about how long it has been there, whether it itches or bleeds, and other questions about the patient's medical history. If skin cancer cannot be ruled out, a sample of the tissue is removed and examined under a microscope (a biopsy). A definitive diagnosis of squamous or basal cell cancer can only be made with microscopic examination of the tumor cells. Once skin cancer has been diagnosed, the stage of the disease's development is determined. The information from the biopsy and staging allows the physician and patient to plan for treatment and possible surgical intervention.
A variety of treatment options are available for those diagnosed with non-melanoma skin cancer. Some carcinomas can be removed by cryosurgery, the process of freezing with liquid nitrogen. Uncomplicated and previously untreated basal cell carcinoma of the trunk and arms is often treated with curettage and electrodesiccation, which is the scraping of the lesion and the destruction of any remaining malignant cells with an electrical current. Removal of a lesion layer-by-layer down to normal margins (Mohs' surgery) is an effective treatment for both basal and squamous cell carcinoma. Radiation therapy is best reserved for older, debilitated patients or when the tumor is considered inoperable. Laser therapy is sometimes useful in specific cases; however, this form of treatment is not widely used to treat skin cancer.
A newer type of radiation treatment for non-melanoma skin cancers consists of low-energy x rays delivered through the tip of a portable needle-like probe at a high dosage rate. This method allows the radiologist to treat the cancer while sparing the surrounding normal skin. The device was effective in treating 83% of skin lesions in a group of patients diagnosed with non-melanomatous skin cancers during a Phase I trial for the Food and Drug Administration (FDA). There were no cases of damage to surrounding tissues.
Some topical (applied onto the skin) creams and ointments may be used to treat certain types of nonmelanoma skin cancers. For example, imiquimod cream, a topical immune stimulator, has been shown effective in treating superficial basal cell carcinoma. The company who marketed the drug was seeking FDA approval.
Alternative medicine aims to prevent rather than treat skin cancer. Vitamins have been shown to prevent sunburn and, possibly, skin cancer. Some dermatologists have suggested that taking vitamins E and C may help prevent sunburn. In one particular study, men and women took these vitamins for eight days prior to being exposed to ultraviolet light. The researchers found that those who consumed vitamins required about 20% more ultraviolet light to induce sunburn than did people who didn't take vitamins. This is the first study that indicates the oral use of vitamins E and C increases resistance to sunburn. These antioxidants are thought to reduce the risk of skin cancer, and are expected to provide protection from the sun even in lower doses. Other anitoxidant nutrients, including beta carotene, selenium, zinc, and the bioflavonoid quercetin have been suggested as possibly preventing skin cancer. However, a 2003 study reported that selenium was not effective in preventing basal cell carcinoma and may even increase risk of squamous cell carcinoma and total nonmelanoma skin cancer. Antioxidant herbs such as bilberry (Vaccinium myrtillus ), hawthorn (Crataegus laevigata ), tumeric (Curcuma longa ), and ginkgo (Ginkgo biloba ) also have been presented as helpful in preventing skin cancers.
A team of researchers at Duke University reported in 2003 that topical application of a combination of 15% vitamin C and 1% vitamin E over a four-day period offered significant protection against sunburn. The researchers suggest that this combination may protect skin against aging caused by sunlight as well.
Another antioxidant that appears to counter the effects of severe sun exposure is superoxide dismutase, or SOD. SOD must be given in injectable form, however, because it is destroyed in the digestive tract.
As of 2003, researchers were also looking at botanical compounds that could be added to skin care products applied externally to lower the risk of skin cancer. Several botanical compounds had been tested on animals and found to be effective in preventing skin cancer, but further research needs to be done in human subjects.
Both squamous and basal cell carcinoma are curable with appropriate treatment, although basal cell carcinomas have about a 5% rate of recurrence. Early detection remains critical for a positive prognosis. Although it is rare for basal cell carcinomas to metastasize, their metastases can rapidly lead to death if they invade the eyes, ears, mouth, or the membranes covering the brain.
Avoiding exposure to the sun reduces the incidence of non-melanoma skin cancer. Sunscreen with a sun-protective factor of 15 or higher is helpful in prevention, along with a hat and clothing to shield the skin from sun damage. People should examine their skin monthly for unusual lesions, especially if previous skin cancers have been experienced.
Advances in photographic technique have now made it easier to track the development of moles with the help of whole-body photographs. A growing number of hospitals are offering these photographs as part of outpatient mole-monitoring services.
Autoimmune— Pertaining to an immune response by the body against one of its own tissues or types of cells.
Curettage— The removal of tissue or growths by scraping with a curette.
Dermatologist— A physician specializing in the branch of medicine concerned with skin.
Electrodesiccation— To make dry, dull, or lifeless with the use of electrical current.
Lesion— A patch of skin that has been infected or diseased.
Topical— Referring to a medication or other preparation applied to the skin or the outside of the body.
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American Academy of Dermatology. 930 N. Meacham Road, P.O. Box 4014, Schaumburg, IL 60168-4014. (847) 330-0230. Fax: (847) 330-0050. 〈http://www.aad.org〉.
Centers for Disease Control and Prevention (CDC). Cancer Prevention and Control Program. 4770 Buford Highway, NE, MS K64, Atlanta, GA 30341. (888) 842-6355. 〈http://www.cdc.gov/cancer/comments.htm〉.
National Cancer Institute (NCI). NCI Public Inquiries Office, Suite 3036A, 6116 Executive Boulevard, MSC8332, Bethesda, MD 20892-8322. (800) 4-CANCER or (800) 332-8615 (TTY). 〈http://www.nci.nih.gov〉.