Most skin cancers are preventable. As they are commonly induced by ultraviolet light, avoidance of excessive sun exposure combined with the use of appropriate clothing and a good sunscreen lotion (SPF 15 or higher in a substantive base that does not easily wash off by sweat or swimming) is recommended.
Risk Factors
Skin cancer is the most common tumour in white populations around the world. The three major types are basal cell carcinoma, squamous cell carcinoma, and cutaneous malignant melanoma. All 3 types of skin cancers are at least twice as common in subjects with light skin hair and eye colour compared to those with dark features (Elwood et al 1984). Other host factors which increase risk of skin cancer, are freckling, presence of large numbers of acquired melanocytic nevi (skin moles), and propensity to burn rather than tan in the sun. (Gallagher et al 1995 a,b)
The most important environmental risk factor for all 3 types of skin cancer is solar ultraviolet radiation (UVR). Solar UVR is thought to account for about 93% of CMM incidence in Canada (Armstrong & Kricker 1994) and, the figure is likely to be similar for non-melanocytic skin cancer.
Childhood sun exposure is thought to be very important in accounting for adult risk of CMM (Khlat et al 1995) as is strong intermittent recreational sun exposure particularly among indoor workers with un-acclimatized skin (Elwood et al 1985). Recently evidence is accumulating that childhood and intermittent recreational exposure are also important in accounting for basal cell carcinoma (Gallagher et al 1995a, Kricker et al 1995).
Squamous cell carcinoma appears to be related more to constant chronic occupational sunlight exposure (Gallagher et al 1995b) than to intermittent exposure.
Studies of exposure to artificial UVR mainly from sun lamps and sun beds, have shown modest increased relative risks for CMM, in the order of 1.1 to 1.2. These results need confirmation in more detailed studies which control for concurrent sun exposure.
Prevention
Use of protective clothing in the summer sun and use of sunscreens are likely to reduce risk of non-melanocytic skin cancers. Not enough evidence is available to indicate whether use of sunscreens will reduce risk of melanoma.
General population screening for cutaneous malignant melanoma is not recommended as no trials have demonstrated that such screening decreases mortality. Subjects with a strong family history of melanoma (2 or more first degree relatives with the disease) may carry a p16 germline mutation predisposing to the disease. These individuals and individuals with atypical nevus syndrome (formerly Dysplastic Nevus Syndrome) should be under regular surveillance by a dermatologist.
References:
Armstrong BK, Kricker A. How much melanoma is caused by sun? Melanoma Res. 1993;3:395-401.
Elwood JM, Gallagher RP, Hill GB, et al. Pigmentation and skin reaction to sun as risk factors for cutaneous melanoma: Western Canada Melanoma Study. BMJ 1984;288:99-102.
Elwood JM, Gallagher RP, Hill GB, Pearson JCG. Cutaneous melanoma in relation to intermittent and constant sun exposure-The Western Canada Melanoma Study. Int J Cancer 1985;35:427-433.
Khlat M, Vail A, Parkin M, Green A. Mortality from melanoma in migrants to Australia: variation by age at arrival and duration of stay. Am J Epidemiol. 1992;135:1103-1113.
Gallagher RP, Hill GB, Bajdik CD, et al. Sunlight exposure, pigmentation factors, and risk of non-melanocytic skin cancer I. Basal cell carcinoma. Arch Dermatol 1995;131:157-163.
Gallagher RP, Hill GB, Bajdik CD, et al. Sunlight exposure, pigmentation factors, and risk of non-melanocytic skin cancer II. Squamous cell carcinoma. Arch Dermatol 1995;131:164-169.
Sun Protection
Sun protection is important for people of all ages.
The relationship between skin cancer and sun exposure is well accepted. However, the exact path between sun exposure and skin cancer is still not completely known. Recently the incidence of basal cell carcinoma has been associated with sun exposure during early childhood. Actinic keratosis and squamous cell carcinoma increase with cumulative sun exposure. The rate of malignant melanoma appears greater in people with intense intermittent sun exposure and increases as one approaches the equator.
UVB (280-320 nanometers) is responsible for most sunburns and the carcinogenic effects of sunlight and UVA (320-400 mm) is responsible mainly for tanning, although in high doses it can burn. UVB penetration is limited to the epidermis whereas UVA, a co-carcinogen also penetrates deeper into the dermis and is likely the major cause of photo-aging.
Sunscreens are very effective at preventing sunburn (UVB protection) and most also contain UVA screens. Those that contain Parsol 1789 protect best for UVA. Sunscreens absorb into the skin and vanish once applied unlike sunblocks which are opaque. Sunblocks contain micronized zinc oxide or titanium dioxide. These physical agents prevent light from reaching the skin thus they will leave a white or tinted film after application. Sunscreens are effective immediately upon application and many are waterproof.
SPF (sun protective factor) is a laboratory derived value of UVB protection. At present there is no similar rating of UVA protection. A SPF of 15 means someone will require 15 times the usual amount of UVB to cause a sunburn, that is if one usually burns in 15 minutes, with a sunscreen SPF 15 they would need 15 x 15 minutes or 225 minutes to burn. SPF 30 is the minimum recommended. Most people do not apply enough sunscreen. Those products with lower SPFs do not protect adequately.
It is generally accepted that sunscreen use lowers the risk of skin cancer, however, there is no epidemiologic confirmation yet.
Perhaps more important than sunscreens is an effort to reduce excessive exposure. Clothing helps, the tighter the weave and more opaque the fabric, the better the sun protection. Hats with broad brims are much more effective than peaked caps. Shade also helps, but alone may only diminish UV exposure by 30%. Since UV is most intense between the hours of 10.00 a.m. and 4.00 p.m., plan outdoor activities outside these hours when possible.
Effective sun protection encompasses behaviour change and includes all the options outlined.
