Chapter 49 Sunscreens and prevention of skin cancer
1. List some of the important facts about skin cancer.
• In the United States, over 1 million new cases of skin cancer are diagnosed annually, afflicting more people than any other cancer.
• In 2009, according to the American Cancer Society, 68,720 Americans will develop malignant melanoma, and there will be 8,650 melanoma-related deaths.
• Melanoma accounts for about 4% of skin cancer cases, but it causes about 79% of skin cancer deaths.
• The incidence of melanoma is increasing at a rate faster than that of any other cancer, having nearly doubled in the last decade.
American Academy of Dermatology. Available at: http://www.aad.org. Accessed August 3, 2010.
American Cancer Society. Available at: http://www.cancer.org. Accessed August 3, 2010.
Skin Cancer Foundation. Available at: http://www.skincancer.org. Accessed August 3, 2010.
2. How does skin type affect the risk for skin cancer?
Anyone can get skin cancer, although some people are at greater risk than others. The skin phototype (SPT) system was developed to identify people who are prone to develop skin cancer. The SPT system is a six-point scale based on a person’s skin color and ability to tan (Table 49-1). Individuals who fall into SPT groups I and II are at highest risk for the development of skin cancer. These two groups of people are especially prone to develop basal cell and squamous cell carcinoma and are at high risk for developing melanoma. Skin types III and IV are less prone to develop basal cell and squamous cell carcinoma but are still at risk for developing melanoma. Basal cell carcinoma, squamous cell carcinoma, and melanoma are rare in skin types V and VI. If patients in groups V and VI develop melanoma, it usually occurs on the palms and soles (acrolentiginous melanoma) or on mucosal surfaces, such as in the mouth or on the genitalia.
3. What are the other risk factors for skin cancer?
Strong skin cancer risk factors include family history, total cumulative sun exposure, the number of blistering sunburns, multiple atypical moles, immunosuppression, and occupational exposure to coal tar, pitch, creosote, arsenic compounds, or radium. Lifetime cumulative sun exposure directly correlates with basal cell and squamous cell carcinoma risk. Individuals who are exposed to the sun on a daily basis, such as farmers, fishermen, and construction workers, are at high risk for developing nonmelanoma skin cancer. Sunburns are directly related to melanoma risk. One study reported a 2.5- to 6.3-fold increased melanoma risk for a person with a history of three or more blistering sunburns. For this reason, indoor workers such as health care professionals and office workers who experience intense, intermittent sun exposure are more prone to developing melanoma.
4. Do hereditary factors affect skin cancer risk?
Skin cancer appears to have a hereditary component. The prototype syndrome of genetically determined increased skin cancer risk is xeroderma pigmentosum (XP). XP patients suffer from an autosomal recessive defect in DNA repair that results in sun sensitivity and early onset of basal cell carcinoma, squamous cell carcinoma, and melanoma. Although much of the molecular genetics of XP is understood, further study is necessary to better understand the genetics of other types of skin cancer-prone families. However, a useful recommendation is to have all first-degree relatives (parents, siblings, and children) of a skin cancer patient examined for skin cancer and taught sun-protection measures.
5. What age or sex factors are important in skin cancer risk?
• Basal cell and squamous cell carcinoma incidences peak in the seventh decade of life. Melanoma incidence peaks around age 50.
• Overall, men develop more skin cancer than do women, but in the third and fourth decades of life, almost as many women develop skin cancer as men.
• Melanoma occurs most frequently on the chest, shoulders, and back in males and in young women (ages 15 to 29). Melanoma is most commonly found on the legs of adult women 30 years and older.
• For both sexes, basal cell and squamous cell carcinoma develop most often on chronically sun-exposed areas, including the head, neck, shoulders, arms, and hands.
7. What warning signs of possible skin cancer should be looked for in the self-skin exam?
The self-skin exam is an important part of skin cancer prevention for two reasons: Studies have shown that abnormal skin lesions are frequently discovered first by the patient, and skin cancer, when treated early, is curable. Patients should be encouraged to examine their entire skin surface on a monthly basis, remembering to include the scalp and normally non–sun-exposed sites, including the buttocks, genitalia, and feet. Warning signs of a possible skin cancer include
• Any mole or brown spot that changes in size, thickness, or texture or develops an irregular border
8. How is ultraviolet light classified?
Ultraviolet (UV) light is broken down into bands of light according to its physical characteristics and biologic effects:
• UVC: 100 to 290 nm wavelength. High-energy radiation that injures cells through direct DNA damage and the generation of free-radical species. Fortunately, UVC radiation is filtered by atmospheric ozone and does not reach the earth’s surface.
• UVB: 290 to 320 nm wavelength. Midrange radiation that is not completely filtered by atmospheric ozone, called the “burning” rays because it causes sunburn. UVB injures skin cells primarily through formation of DNA thymine dimers and 6 to 4 photoproducts that, if not repaired properly, cause gene mutations and lead to altered cell function and carcinogenesis.
• UVA: 320 to 400 nm wavelength. Long-wave radiation that is the lowest energy spectrum of ultraviolet. UVA is not filtered by atmospheric ozone, and a 150-fold greater amount of UVA strikes the surface of the earth compared to UVB. UVA damages skin cells predominantly through the formation of free radicals. UVB penetrates to the basal layer of the epidermis, whereas UVA penetrates to the middermis. Skin wrinkling following chronic sun exposure is due to UVA injury of dermal fibroblasts, resulting in altered collagen and elastin synthesis.
Table 49-1. Human Skin Phototypes
| SKIN PHOTOTYPE* | UNEXPOSED SKIN COLOR | SUN RESPONSE HISTORY |
|---|---|---|
| I | White | Always burns, never tans |
| II | White | Always burns, tans minimally |
| III | White | Burns minimally, tans gradually and uniformly |
