Excessive exposure to sunlight (i.e., greater exposure than is appropriate for the person’s skin type) is strongly associated with the development of keratinocyte cancer (KC), which includes cutaneous squamous cell carcinoma (cSCC) and basal cell carcinoma (BCC). Within Australia and other large countries such as the USA, the incidence of KC is highest in areas of low latitude (i.e. closest to the equator) and it occurs more frequently on parts of the body that are habitually exposed to sunlight. In particular, cSCC rarely occurs on parts of the body that are not habitually exposed.
Cutaneous squamous cell carcinoma and BCC appear to differ in their relationship to sun exposure. Cutaneous squamous cell carcinoma is related to total lifetime exposure to the sun, but not to the pattern of exposure (intermittent exposure versus more continuous exposure, as occurs in outdoor workers). Outdoor workers appear to have the highest risk. For BCC, in contrast, recreational and intermittent exposure may be more closely related to risk than the total amount of exposure, with indoor workers possibly having higher risk than outdoor workers.
A randomised trial of daily sunscreen use in adults in Queensland showed a reduction in risk of cSCC, and a reduction in BCC risk with longer follow up. Randomised trials of regular sunscreen use showed a reduction in numbers of actinic (solar) keratoses, which are known precursors of cSCC.
Studies of immigrants to Australia from countries with predominately light-skinned populations indicate that excessive sun exposure during childhood and adolescence is very important in causing both BCC and cSCC. For cSCC there is also more direct evidence of the impact of exposure to ultraviolet (UV) radiation early in life. These findings indicate that particular emphasis should be placed on protection from sunlight exposure in childhood and adolescence. However, skin cancer itself is rare before puberty and there may be a long latent period, usually many years, from the initiating sun exposure to the time a skin cancer (especially a cSCC) becomes clinically apparent. Furthermore, while childhood sun exposure is very important in the development of skin cancer, exposure in adult life is also important. Therefore, everyone should be advised to use sun protection measures throughout their life.
Cancer Council Australia does not distinguish between melanoma and keratinocyte cancers in its recommendations on sun protection in the prevention of skin cancer. It recommends that when the solar UV index is 3 or above, people should wear a wide-brimmed hat and clothing to cover exposed skin, wear wrap-around sunglasses, seek shade and use a sunscreen with sun protection factor (SPF) 30 or higher on skin left exposed.
Topics covered in this section include:
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- Scotto J, Kopf AW, Urbach F. Non-melanoma skin cancer among Caucasians in four areas of the United States. Cancer 1974 Oct;34(4):1333-8 Abstract available at http://www.ncbi.nlm.nih.gov/pubmed/4422100.
- English DR, Kricker A, Heenan PJ, Randell PL, Winter MG, Armstrong BK. Incidence of non-melanocytic skin cancer in Geraldton, Western Australia. Int J Cancer 1997 Nov 27;73(5):629-33 Abstract available at http://www.ncbi.nlm.nih.gov/pubmed/9398037.
- English DR, Armstrong BK, Kricker A, Winter MG, Heenan PJ, Randell PL. Case-control study of sun exposure and squamous cell carcinoma of the skin. Int J Cancer 1998 Jul 29;77(3):347-53 Abstract available at http://www.ncbi.nlm.nih.gov/pubmed/9663594.
- Gallagher RP, Hill GB, Bajdik CD, Coldman AJ, Fincham S, McLean DI, et al. Sunlight exposure, pigmentation factors, and risk of nonmelanocytic skin cancer. II. Squamous cell carcinoma. Arch Dermatol 1995 Feb;131(2):164-9 Abstract available at http://www.ncbi.nlm.nih.gov/pubmed/7857112.
- Rosso S, Zanetti R, Martinez C, Tormo MJ, Schraub S, Sancho-Garnier H, et al. The multicentre south European study 'Helios'. II: Different sun exposure patterns in the aetiology of basal cell and squamous cell carcinomas of the skin. Br J Cancer 1996 Jun;73(11):1447-54 Abstract available at http://www.ncbi.nlm.nih.gov/pubmed/8645596.
- Kricker A, Armstrong BK, English DR, Heenan PJ. Does intermittent sun exposure cause basal cell carcinoma? a case-control study in Western Australia. Int J Cancer 1995 Feb 8;60(4):489-94 Abstract available at http://www.ncbi.nlm.nih.gov/pubmed/7829262.
- Kricker A, Armstrong BK, English DR, Heenan PJ. A dose-response curve for sun exposure and basal cell carcinoma. Int J Cancer 1995 Feb 8;60(4):482-8 Abstract available at http://www.ncbi.nlm.nih.gov/pubmed/7829261.
- Green A, Williams G, Neale R, Hart V, Leslie D, Parsons P, et al. Daily sunscreen application and betacarotene supplementation in prevention of basal-cell and squamous-cell carcinomas of the skin: a randomised controlled trial. Lancet 1999 Aug 28;354(9180):723-9 Abstract available at http://www.ncbi.nlm.nih.gov/pubmed/10475183.
- Pandeya N, Purdie DM, Green A, Williams G. Repeated occurrence of basal cell carcinoma of the skin and multifailure survival analysis: follow-up data from the Nambour Skin Cancer Prevention Trial. Am J Epidemiol 2005 Apr 15;161(8):748-54 Abstract available at http://www.ncbi.nlm.nih.gov/pubmed/15800267.
- Darlington S, Williams G, Neale R, Frost C, Green A. A randomized controlled trial to assess sunscreen application and beta carotene supplementation in the prevention of solar keratoses. Arch Dermatol 2003 Apr;139(4):451-5 Abstract available at http://www.ncbi.nlm.nih.gov/pubmed/12707092.
- Naylor MF, Boyd A, Smith DW, Cameron GS, Hubbard D, Neldner KH. High sun protection factor sunscreens in the suppression of actinic neoplasia. Arch Dermatol 1995 Feb;131(2):170-5 Abstract available at http://www.ncbi.nlm.nih.gov/pubmed/7857113.
- Thompson SC, Jolley D, Marks R. Reduction of solar keratoses by regular sunscreen use. N Engl J Med 1993 Oct 14;329(16):1147-51 Abstract available at http://www.ncbi.nlm.nih.gov/pubmed/8377777.
- Kricker A, Armstrong BK, English DR, Heenan PJ. Pigmentary and cutaneous risk factors for non-melanocytic skin cancer--a case-control study. Int J Cancer 1991 Jul 9;48(5):650-62 Abstract available at http://www.ncbi.nlm.nih.gov/pubmed/2071226.
- English DR, Armstrong BK, Kricker A, Winter MG, Heenan PJ, Randell PL. Demographic characteristics, pigmentary and cutaneous risk factors for squamous cell carcinoma of the skin: a case-control study. Int J Cancer 1998 May 29;76(5):628-34 Abstract available at http://www.ncbi.nlm.nih.gov/pubmed/9610717.