SUNSCREENS AND SKIN CANCER PREVENTION 195 trial ceased, this would not have introduced bias but would have diluted the strength of the fi ndings. DISCUSSION AND CONCLUSIONS Although there was evidence that sunscreen may prevent the occurrence of multiple BCCs over time, the apparent lack of protective effect of sunscreen use on BCC occurrence overall may be partly explained by the dispersed anatomic site distribution of BCC, where around one-third occur on sites other than the specifi ed trial application sites [although 25% of the intervention group were applying sunscreen regularly to other sites, namely, the trunk and lower limbs, at the end of the trial (16)]. It could also mean that regular sunscreen use for a limited period in adulthood is “too little, too late” to prevent BCC development if BCCs are initiated early in life and are promoted not only by solar UV radiation but by other factors as well. On the other hand, the large reductions in risk of SCC and melanoma with regular sun- screen use are consistent with other trials (17–20) that have shown regular sunscreen use can prevent development of actinic keratosis [the common benign tumors caused by cu- mulative sun exposure that are strongly associated with both SCC and melanoma (21)] and melanocytic naevi [common pigmented lesions that are the strongest known predic- tors of melanoma risk (22)], respectively. The protective effect of sunscreen on skin cancer is also supported by experimental evidence that consistently shows that application of sunscreen prevents DNA damage in human skin (23). In summary, based on the evidence from a single randomized controlled trial conducted in an Australian community, regular sunscreen use by adults does not appear to protect against BCC but does appear to reduce the risk of developing cutaneous SCC and mela- noma, consistent with other fi ndings. Sunscreen use is but one of a suite of sun protection measures, however, and it is important for healthcare agencies and practitioners to en- courage the use of clothing cover and shade in addition to promoting sunscreen (3). Users also need clear instructions on the proper application and reapplication of sunscreen to achieve optimal protection (16). REFERENCES (1) D. Rigel, Cutaneous ultraviolet exposure and its relationship to the development of skin cancer, J. Am. Acad. Dermatol., 58, S129–S132 (2008). (2) A. C. Green, C. M. Olsen, and D. Hunter, “Epidemiology of cancer of the skin,” in A Textbook of Can- cer Epidemiology and Control, 3rd Ed., A. Adami, A. Trichopoulos, and D. Hunter. Eds. (Oxford University Press, New York, NY, 2018), pp. 355–381. (3) M. Janda and A. C. Green, “Primary prevention of skin cancer”, in Evidence-Based Dermatology, 3rd Ed., H. Williams, M. Bigby, A. Herxheimer, L. Naldi, B. Rzany, R. Dellaville, Y. Ran, and F. Furue. Eds. (Wiley-Blackwell, Hoboken, NJ, 2014), pp. 223–230. (4) C. S. Rueegg, J. S. Stenehjem, M. Egger, R. Ghiasvand, E. Cho, E. Lund, E. Weiderpass, A. C. Green, and M. B. Veierod, Challenges in assessing the sunscreen melanoma association, Int. J. Canc., 144, 2651–2668 (2019). (5) A. C. Green and G. M. Williams, Sunscreen use is a safe and effective approach to skin cancer preven- tion, Cancer Epidemiol. Biomark. Prev., 16, 1921–1922 (2007). (6) A. Green, D. Battistutta, V. Hart, D. Leslie, G. Marks, G. Williams, P. Gaffney, P. Parsons, L. Hirst, F. Frost, E. Orrell, K. Durham, and C. Lang The Nambour Prevention Study Group, Nambour skin cancer and

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