Link between UV and cancer

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Link between UV and cancer

Sun exposure

The major cause of melanoma and NMSC is UV radiation exposure[1]. Childhood and adolescent sun exposure is thought to be important in determining the lifetime potential for skin cancer. Adult exposure appears to contribute to the extent to which this potential is realised. The exact exposure needed to develop various skin cancers is not entirely clear. It is likely that both episodic and cumulative exposures are important; episodic exposures have been shown to more strongly determine the risk of melanoma. Based on a review of recalled sun exposure by period of life in studies of melanoma, the relative risk of melanoma with a history of childhood sunburn has been estimated to be 1.8, while for sunburn in adulthood it is 1.5[2].

In adult life, recreational (intermittent) sun exposure appears to be the strongest determinant of melanoma risk, followed by total lifetime sun exposure and occupational exposure. Fair skin, which tends to burn easily and rarely tans, is also an important risk factor for skin cancer[1].

In relation to NMSC, there is evidence that childhood and recreational (that is intermittent and non-occupational) sun exposure is important in determining the risk of basal cell carcinoma (BCC), while cumulative sun exposure such as occupational exposure, is the main determinant for squamous cell carcinoma (SCC)[1].

Using actinic keratoses as a surrogate for NMSC, studies have shown the impact of childhood exposure on increasing the risk of NMSC[3]; sunscreen use has been shown to reduce the risk in adults[4][5].

The burden of NMSC depends on geographical location. In Australia, both BCC and SCC rates are around three times higher in latitudes closer to the equator[6][7], where UV radiation is higher.


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Solariums

In 2009, the International Agency for Research on Cancer (IARC) added UV emitting tanning beds to its highest cancer risk category, labelling them as "carcinogenic to humans" after deeming them to be more dangerous than previously suggested[8]. A systematic review of published studies revealed that first exposure to a solarium before the age of 35 years increases the risk of cutaneous melanoma by 75%[9]. For all users, the risk of squamous cell carcinoma is estimated to be more than double compared with non-users[9].

The Australian/New Zealand standard for the solarium industry (AS/NZS 2635:2008) was revised in January 2009. The standard covers the operation of solariums and provides best practice industry guidelines, such as excluding individuals with skin type I (pale white skin that always burns, never tans) and those under 18 years of age. It also recommends that individuals with skin type II (people with white skin who burn easily, tan minimally) should not use a tanning unit.

There is no evidence supporting the view that exposure to UV radiation through solariums is ‘safe’ or that tanning in this way protects against skin cancer. The Australian/New Zealand standard for the solarium industry prohibits any claims of health benefits and ensures warning signs listing the risks must be exhibited.

See the Cancer Council position statement on Solariums for more information


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Impact of climate change

The ozone layer acts as a barrier to UV radiation; its depletion over the 20th century has resulted in higher radiation levels reaching the earth’s surface. International measures to protect the ozone layer are showing signs of impact, but improvements have not yet returned ozone to pre-1970s levels[10][11].

Recently there has been an increased awareness of the interactions between ozone depletion and climate change, with global warming also thought to slow the recovery of the ozone layer[10]. It is estimated that the increase in ambient temperature due to climate change will influence people’s behaviour and the time they spend outdoors. Therefore, skin cancer incidence is likely to continue to rise, particularly in temperate climates. Previous research has shown that people are more likely to be sunburnt in warmer weather[12][13].


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Sunscreens: the evidence

There has been some debate about the role of sunscreens in skin cancer prevention and the potential association of sunscreen use with melanoma risk. Follow-up on a randomised trial published in 2010 concluded that melanoma may be preventable in adults by regular use of sunscreen[14]. A review found mounting evidence that sunscreen can prevent SCC, but no evidence that it can prevent BCC[15]. A summary of the evidence published in 2007 also found no conclusive evidence that broad spectrum sunscreens prevented BCC[16].

It has also been suggested that people may use sunscreen in order to stay longer in the sun (by reducing the risk of burning), thus increasing their risk of cutaneous melanoma[17][18]. However, Gallagher et al. caution that retrospective case–control studies of melanoma and sunscreen use should be interpreted with great care, because of subject recall problems and the inevitable confounding of sunscreen use with reduced exposure[15].

Daily sunscreen use has been shown to be both effective and cost-efficient in preventing squamous cell carcinomas and solar keratoses[19][20]. An Australian study estimated that there were 14,200 fewer cases of squamous cell carcinoma diagnosed in 2008 due to sunscreen use[21]. The same study also found about 14% of people (or 1,729 cases) who would otherwise have developed melanoma in 2008 had their cancers prevented through regular sunscreen use[21]. While more evidence is needed to show that modern sunscreens prevent melanoma, their use, along with other sun protection strategies, is encouraged as a means of combating the year-on-year rise in melanoma incidence[22].

Nanotechnology has been used in sunscreens for many years. All sunscreens in Australia are tightly regulated through the Therapeutic Goods Administration (TGA). In early 2009, the TGA reviewed the scientific literature in relation to the use of nanoparticulate zinc oxide and titanium dioxide in sunscreens, concluding that:

  • The potential for titanium dioxide and zinc oxide nanoparticles in sunscreens to cause adverse effects depends primarily upon the ability of the nanoparticles to reach viable skin cells; and
  • The current weight of evidence suggests that titanium dioxide and zinc oxide nanoparticles do not reach viable skin cells; rather, they remain on the surface of the skin and in the outer layer of the skin composed of non-viable cells.

Drawing on the best available evidence, our current assessment is that nanoparticulates used in sunscreens do not pose a risk. However, Cancer Council Australia continues to monitor research and welcomes any new data that sheds more light on the topic.


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References

  1. 1.0 1.1 1.2 Armstrong B. How sun exposure causes skin cancer: An epidemiological perspective. In: Hill D, Elwood JM, English DR. Prevention of Skin Cancer. Dordrecht, Netherlands: Kluwer Academic Publishers; 2004. p. 89-116.
  2. Whiteman DC, Whiteman CA, Green AC. Childhood sun exposure as a risk factor for melanoma: a systematic review of epidemiologic studies. Cancer Causes Control 2001 Jan;12(1):69-82 Abstract available at http://www.ncbi.nlm.nih.gov/pubmed/11227927.
  3. Marks R, Jolley D, Lectsas S, Foley P. The role of childhood exposure to sunlight in the development of solar keratoses and non-melanocytic skin cancer. Med J Aust 1990 Jan 15 [cited 32202 Jan 1];152(2):62-6 Abstract available at http://www.ncbi.nlm.nih.gov/pubmed/2296232.
  4. 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.
  5. Green A, Battistutta D, Hart V, Leslie D, Weedon D. Skin cancer in a subtropical Australian population: incidence and lack of association with occupation. The Nambour Study Group. Am J Epidemiol 1996 Dec 1;144(11):1034-40 Abstract available at http://www.ncbi.nlm.nih.gov/pubmed/8942434.
  6. National Cancer Control Initiative. A report by the National Cancer Control Initiative Non-melanoma Skin Cancer Working Group for the state and territory cancer councils. Carlton: NCCI; 2003 Nov Available from: http://canceraustralia.gov.au/sites/default/files/publications/nmscreport1_504af01fd661f.pdf.
  7. Staples M, Marks R, Giles G. Trends in the incidence of non-melanocytic skin cancer (NMSC) treated in Australia 1985-1995: are primary prevention programs starting to have an effect? Int J Cancer 1998 Oct 5;78(2):144-8 Abstract available at http://www.ncbi.nlm.nih.gov/pubmed/9754642.
  8. WHO International Agency for Research on Cancer Monograph Working Group, El Ghissassi F, Baan R, Straif K, Grosse Y, Secretan B, et al. A review of human carcinogens--part D: radiation. Lancet Oncol 2009 Aug;10(8):751-2 Abstract available at http://www.ncbi.nlm.nih.gov/pubmed/19655431.
  9. 9.0 9.1 International Agency for Research on Cancer Working Group on artificial ultraviolet (UV) light and skin cancer. The association of use of sunbeds with cutaneous malignant melanoma and other skin cancers: a systematic review. Int J Cancer 2007 Mar 1;120(5):1116-22 Abstract available at http://www.ncbi.nlm.nih.gov/pubmed/17131335.
  10. 10.0 10.1 Andrady AL, Aucamp PJ, Bais AF, Ballaré CL, Bjorn LO, Bornman JF, et al. Environmental effects of ozone depletion: 2006 assessment: interactions of ozone depletion and climate change. Executive summary. Photochem Photobiol Sci 2007 Mar;6(3):212-7 Abstract available at http://www.ncbi.nlm.nih.gov/pubmed/17344958.
  11. Li F, Stolarski RS, Newman PA. Stratospheric ozone in the post-CFC era. Atmos. Chem. Phys 2009;9, 2207-13 Abstract available at http://www.atmos-chem-phys.net/9/2207/2009/acp-9-2207-2009.html.
  12. Dobbinson SJ, Wakefield MA, Jamsen KM, Herd NL, Spittal MJ, Lipscomb JE, et al. Weekend sun protection and sunburn in Australia trends (1987-2002) and association with SunSmart television advertising. Am J Prev Med 2008 Feb;34(2):94-101 Abstract available at http://www.ncbi.nlm.nih.gov/pubmed/18201638.
  13. Hill D, Boulter J. Sun protection behaviour – determinants and trends. Cancer Forum 1996;20(3), 204-11.
  14. Green AC, Williams GM, Logan V, Strutton GM. Reduced melanoma after regular sunscreen use: randomized trial follow-up. J Clin Oncol 2011 Jan 20;29(3):257-63 Abstract available at http://www.ncbi.nlm.nih.gov/pubmed/21135266.
  15. 15.0 15.1 Gallagher R, Lee T, Bajdik C. Sunscreens: can they prevent skin cancer? In: Hill D, Elwood JM, English DR. Prevention of Skin Cancer. Dordrecht, Netherlands: Kluwer Academic Publishers; 2004. p. 141-56.
  16. Green AC, Williams GM. Point: sunscreen use is a safe and effective approach to skin cancer prevention. Cancer Epidemiol Biomarkers Prev 2007 Oct;16(10):1921-2 Abstract available at http://www.ncbi.nlm.nih.gov/pubmed/17932337.
  17. Autier P. Sunscreen abuse for intentional sun exposure. Br J Dermatol 2009 Nov;161 Suppl 3:40-5 Abstract available at http://www.ncbi.nlm.nih.gov/pubmed/19775356.
  18. International Agency for Research on Cancer Working Group. Sunscreens, IARC Handbook of Cancer Prevention, Volume 5. Lyon, France: IARC; 2001.
  19. Gordon LG, Scuffham PA, van der Pols JC, McBride P, Williams GM, Green AC. Regular sunscreen use is a cost-effective approach to skin cancer prevention in subtropical settings. J Invest Dermatol 2009 Dec;129(12):2766-71 Abstract available at http://www.ncbi.nlm.nih.gov/pubmed/19536149.
  20. van der Pols JC, Williams GM, Pandeya N, Logan V, Green AC. Prolonged prevention of squamous cell carcinoma of the skin by regular sunscreen use. Cancer Epidemiol Biomarkers Prev 2006 Dec 1;15(12):2546-8 Abstract available at http://www.ncbi.nlm.nih.gov/pubmed/17132769.
  21. 21.0 21.1 Olsen CM, Wilson LF, Green AC, Bain CJ, Fritschi L, Neale RE, et al. Cancers in Australia attributable to exposure to solar ultraviolet radiation and prevented by regular sunscreen use. Aust N Z J Public Health 2015 Oct;39(5):471-6 Abstract available at http://www.ncbi.nlm.nih.gov/pubmed/26437734.
  22. Diffey BL. Sunscreens as a preventative measure in melanoma: an evidence-based approach or the precautionary principle? Br J Dermatol 2009 Nov;161 Suppl 3:25-7 Abstract available at http://www.ncbi.nlm.nih.gov/pubmed/19775353.

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