Sunscreens and Prevention of Skin Cancer

1

List some important facts about skin cancer

• About 90% of nonmelanoma skin cancers are related to ultraviolet (UV) radiation from the sun.

• More than 5.4 million cases of nonmelanoma skin cancer were treated in over 3.3 million people in the United States during 2012, the most recent year for which data is available.

• Basal cell carcinoma, a form of nonmelanoma skin cancer, if the commonest cancer of mankind.

• One in five Americans will develop skin cancer by age 70.

• Melanoma makes up less than 2% of all skin cancers, but it causes most skin cancer deaths.

• On average, a person’s risk for melanoma doubles if he or she has had more than five sunburns and just one blistering sunburn in childhood or adolescence more than doubles a person’s chances of developing melanoma later in life.

• New melanoma cases diagnosed in 2019 will increase by 7.7%, but the number of melanoma deaths is expected to decrease by 22% in 2019.

Skin Cancer Foundation. Available at: http://www.skincancer.org . Accessed October 11, 2019.

2

How does skin type affect the risk for skin cancer?

Anyone can get skin cancer, but certain people are at higher risk. The Fitzpatrick Phototyping Scale is used to identify people prone to developing skin cancer. This is a six-tiered scale based on skin color and ability to tan ( Table 48.1 ). Individuals in groups I and II are at highest risk for developing basal and squamous cell carcinomas, and melanoma. Skin types III and IV are less prone to develop basal and squamous cell carcinomas 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 acral skin (acrolentiginous melanoma) or on mucosal surfaces, such as in the mouth or genitalia.

3

What are the other risk factors for skin cancer?

Skin cancer risk factors include family history, cumulative sun exposure, history of blistering sunburns, multiple atypical moles, immunosuppression, and occupational exposures (coal tar, pitch, creosote, arsenic compounds, or radium). Lifetime cumulative sun exposure directly correlates with basal and squamous cell carcinomas risk. Sunburns, particularly in youth, and the number of nevi (moles) and atypical nevi (unusual appearing moles) are 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 in youth.

4

What body sites are at highest risk for skin cancer?

• Melanoma occurs most frequently on the chest, shoulders, and back in men and in young women (ages 15 to 29). Melanoma is most often found on the legs of women 30 years of age and older.

• For both sexes, basal and squamous cell carcinomas develop most often on chronically sun-exposed areas, including the head, neck, shoulders, arms, and hands.

5

What should health care providers teach patients about skin cancer?

Providers should emphasize two things: 1) prevention and 2) early detection. The most important strategy for preventing skin cancers, including melanoma, is reducing unnecessary exposure to UV light. Unfortunately, some skin cancer risk factors, such as skin color type, are not modifiable. Nearly all skin cancers, even melanoma, are curable when detected early. Early detection of skin cancers is possible through monthly skin self-examination. Patients should be encouraged to examine their entire skin surface on a monthly basis, including the scalp and non–sun-exposed sites, like the buttocks, genitalia, and feet. New or changing lesions should be evaluated by a professional provider.

6

What are warning signs of possible skin cancer?

• An open sore that does not heal in 3 weeks

• A spot or sore that persistently itches, burns, stings, crusts, scabs, or bleeds

• Any “mole” or pigmented lesion that changes in color, size, thickness, texture or develops irregular borders

• Any skin lesion that appears different or “stands out” from the other lesions on a patient (the so-called “ugly duckling” sign)

7

How is UV light classified?

UV light (UV radiation [UVR]) is classified based on wavelength, according to its physical characteristics and biologic effects:

• UVC: 100- to 280-nm wavelength. UVC radiation is filtered by atmospheric ozone and does not reach the earth's surface.

• UVB: 280- to 315-nm wavelength. Midrange radiation that is incompletely filtered by atmospheric ozone

• UVA: 315- to 400-nm wavelength. Longer-wave UVR that is further subdivided into UVA-1 (340 to 400 nm) and UVA-2 (315 to 340 nm). UVA is not filtered by atmospheric ozone, and 150-fold greater amount of UVA reaches the earth’s surface, compared to UVB.

8

How do UVA and UVB affect the skin?

UVB penetrates to the basal layer of epidermis and injures skin cells through the formation of DNA thymine dimers and 6-4 photoproducts. If not repaired, these can genetic mutations and lead to altered cell function and skin cancer. UVB is also responsible for causing sunburn.

UVA, being a longer wavelength, penetrates deeper into the skin. UVA damages skin cells predominantly through formation of free radicals. Chronic exposure results in photoaging, such as skin wrinkling, solar lentigines, poikiloderma, telangiectasia, and altered collagen and elastin.

Both UVA and UVB are carcinogenic. Mnemonic: UVB causes sunburn (UV B = B urn), UVA causes aging (UV A = A ging).