Prevalence and Risk Factors. About 160,000 people develop squamous cell carcinomas every year. The incidence of this cancer is increasing.
Sun exposure and sun damage are the greatest risk factors, and the addition of other factors compound the risk:
- Older age.
- Being fair skinned, particularly having red hair.
- Living in sunny climates.
- Treatments for psoriasis -- including PUVA (psoralen and UVA radiation) and immunosuppressant agents, such as cyclosporine -- also pose a risk for squamous cell carcinoma (SCC). [A 2005 study found that the rheumatoid arthritis drug etanercept (Enbrel) does not increase squamous cell cancer risk.]
- Genital warts (human papillomavirus) may also increase the risk in the genital and anal areas and around fingernails.
Outlook and Severity. Prompt treatment is desirable because squamous cell carcinomas are more likely to spread to local lymph nodes than are basal cell carcinomas, the other common skin cancer. Mortality rates for this cancer are very low, although squamous cell cancer still kills between 2,000 and 2,500 Americans each year. The risk for metastases (the spread of cancer to other organs) ranges from 0.5% to 16%, depending on risk factors. Squamous cell carcinomas most likely to spread include the following:
- Deep lesions, those larger than 2 cm in diameter, or patches with poorly defined margins.
- Recurrent lesions.
- SCC on neck, earlobe, eyelid, lips, or temple.
- SCC that develop in ulcers.
- SCC that develops on skin areas that have been previously treated with radiation or exposed to carcinogenic chemicals.
People with squamous cell carcinomas seem to be at higher risk for other cancers, including melanoma itself, lung cancer, non-Hodgkin lymphoma, bladder cancer, leukemia, testicular and prostate cancer in men, and breast cancer in women.
Precancerous Skin Disorders
Actinic (Solar) Keratoses. Actinic (also called solar) keratoses are the most common of all precancerous skin lesions. In fact, evidence now strongly supports the belief that actinic keratoses are actually squamous cell carcinomas in situ (the early stage of SCC). It should be noted, however, that not all actinic keratoses progress to carcinomas. One long-term study in 1999 indicated that the rate of malignant transformation might be about 10% over a 10-year period, while other studies show higher rates of progression to SCC.
Actinic keratoses occur after years of sun exposure and afflict over half of Caucasians aged 40 or older who live in hot, sunny climates. They occur predominantly on sun-exposed skin such as the face, neck, back of the hands and forearms, upper chest, and upper back. Men may develop keratoses along the rim of the ear.
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