Non-melanoma skin cancer is a malignant growth of the external surface or epithelial layer of the skin.
Skin cancers are the most common type of cancer by far in the United States. Approximately 800,000 to 900,000 new cases of basal cell skin cancer are diagnosed each year. Squamous cell skin cancers are diagnosed less frequently with 200,000 to 300,000 new cases diagnosed annually. The number of new cases of non-melanoma skin cancers is increasing each year. This increase is attributed to improved detection capabilities, increased exposure to the sun, and increase in the lifespan of the general population. Most of the time, basal cell and squamous cell skin cancers are not fatal. The American Cancer Society reports a decline of about 30% in deaths from skin cancer between 1980 and 2010.
Exposure to sunlight is documented as the main cause of more than 1 million cases of non-melanoma skin cancers diagnosed each year in the United States. Incidence increases for those living where direct sunshine is plentiful, such as near the equator.
Ultraviolet B (UVB) rays are thought to cause most basal cell and squamous cell skin cancers. Ultraviolet A (UVA) rays may also directly cause some skin cancers. In addition to sunlight, overexposure to UVB rays can occur from the use of tanning booths and beds and from sunlamps.
People who are at highest risk for the development of skin cancer include individuals who have fair skin and light-colored eyes and who freckle or burn easily when exposed to UVB rays.
Other individuals at high risk include older adults because exposure increases over time. Males are two to three times as likely to develop skin cancer as females. Exposure to chemicals such as arsenic, industrial tar, coal, paraffin, and certain types of oil can lead to skin cancer. Other risk factors include a history of smoking, a history of previous skin cancer, and history of illnesses, diseases, or conditions which impair immunity.
Other types of skin cancers that occur less frequently are: Merkel cell carcinoma, Kaposi sarcoma, cutaneous lymphoma, skin adenexal tumors, and various types of sarcomas. Combined, the incidence of all of these rarer types of non-melanoma skin cancer account for less than 1% of skin cancer.
Basal cell carcinoma affects the skin's basal layer and has the potential to grow progressively larger, although it rarely spreads to distant areas (metastasizes). Basal cell carcinomas account for 80% of skin cancers (excluding melanoma), whereas squamous cell cancer makes up about 20%. Basal cell cancer tends to recur, with approximately 50% of people diagnosed with basal cell cancer developing a new skin cancer within five years. Squamous cell carcinoma is a malignant growth of the external surface of the skin. Squamous cell cancers metastasize at a rate of 2% to 6%, with up to 10% of lesions affecting the ear and lip. Squamous cell carcinomas appear to be more aggressive than basal cell cancers.
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 common in people over 40.
About 1–% 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 to 6 millimeters 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 is characterized by a small, scaling, raised bump on the skin with a crusting ulcer in the center, but without pain and itching. The lesion may also appear as flat, reddish, slow-growing patches.
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, individuals taking 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, tumor cells can spread (metastasize) to muscle, bone, nerves, and possibly the brain.
To diagnose skin cancer, clinicians 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. Lymph nodes in the vicinity of the suspicious lesion will be palpated.
The patient may be referred to a dermatologist for a more comprehensive examination. The dermatologist may use a device known as a dermatoscope to visualize spots on the skin more clearly.
If skin cancer cannot be ruled out, a sample of 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. Removal of larger tumors may require skin grafting and reconstructive surgery.
Treatments for non-melanoma skin cancer also include photodynamic therapy (PDT), topical chemotherapy in which the anticancer drug is applied to the lesion as an ointment or as a cream, laser surgery, and the use of drugs such as imiquimod and interferon. These drugs are classified as immune response modifiers. The drugs work to boost the body's immune system to help decrease the size of the lesion and sometimes are effective in eliminating the skin cancer altogether.
Radiation therapy is best reserved for older, debilitated patients or when the tumor is considered inoperable.
Both squamous and basal cell carcinoma are curable with appropriate treatment, although basal cell carcinomas have a higher rate of recurrence. Early detection remains critical for a positive prognosis. Although it is rare for basal cell carcinomas to metastasize, metastases can rapidly lead to death if the tumor cells invade the eyes, ears, mouth, or the membranes covering the brain.
Not all skin cancers can be prevented. However, there are ways to reduce risk for skin cancer. Avoiding exposure to the sun reduces the incidence of nonmelanoma skin cancer. Sunscreen and sunblock preparations provide protection against both UVA and UVB rays. These preparations should also be rated with a sun protection factor (SPF) of 30 or higher. They should be applied 30 minutes before going outdoors and then reapplied every two hours and after swimming. Other recommended practices are to wear a hat, sunglasses, and clothing to shield the skin from sun damage. The lips should be protected by wearing lip balm with sunscreen.
Other strategies include avoiding the outdoors during times of maximum UV effects which is typically between the hours of 10 A.M. until 4 P.M. especially on days when the UV index is high. People can check online at www.epa.gov/sunwise/uvindex.html to determine the UV index in their area on any particular day. Avoiding tanning beds, tanning booths, and sunlamps is also strongly recommended. Adults should consider applying protective wear for children. Such wear is designed to cover the child from the neck to the knees with sun-protective fabric.
People should examine their skin monthly for unusual lesions, especially if previous skin cancers have been experienced.
See also Cancer ; Melanoma ; Smoking .
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Rigel, Darrel S., et al. Cancer of the Skin: Expert Consult. 2nd ed. Philadelphia: Saunders, 2011.
Cafardi, J. A., et al. “Prospects for Skin Cancer Treatment and Prevention: The Potential Contribution of an Engineered Virus.” Journal of Investigative Dermatology 131, no. 3 (2011): 559–61.
Lomas, A., et al. “A Systematic Review of Worldwide Incidence of Nonmelanoma Skin Cancer.” British Journal of Dermatology 166, no. 5 (2012): 1069–80.
Patel, R. V., A. Frankel, and A. Goldenberg. “An Update on Nonmelanoma Skin Cancer.” Journal of Clinical and Aesthetic Dermatology 4, no. 2 (2011): 20–7.
Tan, S., C. Sinclair, and P. Foley. “Running Behind a Tourist: Leisure-related Skin Cancer Prophylaxis.” British Journal of Dermatology 167, Suppl. 2 (2012): 70–5.
American Academy of Dermatology (AAD), PO Box 4014, Schaumburg, IL, 60168, (866) 503-7546, MRC@aad.org, http://www.aad.org .
American Cancer Society, 250 Williams St., Atlanta, GA, 30303, (800) 227-2345, http://www.cancer.org .
Jeffrey P. Larson, RPT
Ken R. Wells
Revised by Melinda Granger Oberleitner, RN, DNS, APRN, CNS