Who Gets It
People who have fair skin, blond or red hair, and blue, green or gray eyes are at increased risk of developing the disease. But so is anyone with a history of substantial sun exposure. Those whose occupations require long hours outdoors or who spend extensive leisure or recreation time in the sun (especially playing golf or other sports) are in particular jeopardy. Anyone who has had basal cell carcinoma is also more likely to develop SCC.
Squamous cell carcinomas are at least twice as frequent in men as in women, partly because of more time spent in the sun. Most SCCs appear in people over age 50, but in recent years more and more young people in their 20s and 30s are being diagnosed with the disease. The number of women under age 40 diagnosed with SCC has especially increased in the last 30 years, and many experts attribute this to their greater use of indoor tanning. More than 419,000 cases of skin cancer in the US each year are linked to indoor tanning, and over 70 percent of tanning salon patrons are female.
The majority of skin cancers in African Americans are squamous cell carcinomas, usually arising on the sites of preexisting inflammatory skin conditions or burn injuries. While people who have dark skin tones are less likely to get skin cancer than people who have light skin tones, it is still essential for them to practice sun protection. All skin types are at risk of skin cancer. Recently, there has been a large increase in new SCCs diagnosed in Latinos and other people of color.
While cumulative exposure to sunlight causes most cases of squamous cell carcinoma, frequent use of indoor tanning also multiplies the risk of SCC; people who use tanning beds are 2.5 times more likely to develop SCC than those who don’t. Skin injuries are another important source. The cancer can arise in burns, scars, ulcers, long-standing sores and sites previously exposed to X-rays or certain chemicals (such as arsenic and petroleum by-products).
People with a UV-sensitive condition such as xeroderma pigmentosum, which makes them more prone to sun damage, are more vulnerable to the disease, as are those with reduced immune system functioning due to a medical condition such as HIV or to certain medical treatments such as chemotherapy or antirejection drugs used after transplant surgery. Organ transplant patients are approximately 100 times more likely than the general public to develop squamous cell carcinoma.
Chronic infections and skin inflammation can also give rise to squamous cell carcinoma. Even excessive sun exposure itself weakens the immune system, making it harder to fight off disease and thus increasing the risk of developing squamous cell carcinoma and other skin cancers. Occasionally, squamous cell carcinomas arise spontaneously on what appears to be normal, healthy skin. Some researchers believe the tendency to develop these cancers can be inherited.
Precancers, the First Step
Certain potentially precancerous growths, or precancers, most of them resulting from cumulative sun damage, can be associated with the later development of squamous cell carcinoma.
Actinic, or Solar, Keratoses
These rough, scaly, slightly raised growths, ranging in color from brown to red and from about 1 mm to 1 inch in diameter, are found on sun-exposed areas of the body, most often in older people. They can be the first step on the road to squamous cell carcinoma, and some experts even consider them the earliest form of SCC. From two to ten percent of untreated actinic keratoses (AKs) advance to squamous cell carcinoma, sometimes within two years, according to different studies. Indeed, 40 to 60 percent of squamous cell carcinomas begin as untreated actinic keratoses. The more AKs that go untreated and the older these lesions are, the greater the chance that one or more may develop into invasive SCC.
AKs are often palpable before becoming visible, and can be felt by running your fingers over sun-exposed areas; this can provide an early sign of their development.
This form of actinic keratosis occurs most often on the lower lip, causing it to become dry, cracked, scaly and pale or white. Why the lower lip? Because it receives more sun exposure than the upper lip. If not treated promptly, actinic cheilitis can lead to squamous cell carcinoma on the lip. If your lips are frequently chapped or burning, you may have actinic cheilitis.
Arising in the mucous membranes, these white patches on the tongue, gums, cheeks, or elsewhere inside the mouth have the potential to develop into squamous cell carcinoma. They may be caused by sources of chronic irritation, such as habitual alcohol consumption or tobacco use, or rough edges on teeth or dentures. They may even be caused by a long-time habit of biting the inside of the lip; however, leukoplakias on the lips are mainly caused by sun damage.
This is now generally considered an early, noninvasive stage of squamous cell carcinoma. It appears as a persistent red-brown, scaly patch that may resemble psoriasis or eczema. If untreated, it may invade deeper structures. Bowen’s disease is most often caused by exposure to the sun or to arsenic, but radiation and other chemical carcinogens, genetics and trauma also may play a role. The human Papillomavirus (HPV), highly transmissible through sexual contact, has been documented as a cause of one form of Bowen’s disease affecting the genitals. HPV can also arise in the mucous membranes of the nose and mouth as well as on the skin. The FDA approved an HPV vaccine for use by females aged 9–26 in 2006, and one for 9-26-year-old males (as well as another vaccine for females) in 2009. The vaccines are considered highly effective in preventing HPV and thereby reducing the risk of both genital warts and cervical cancer as well as Bowen’s disease.