br Ethical approval and consent to participate
Ethical approval and consent to participate
Conflict of interest statement
Acknowledgements The authors would like to thank Dr Jeremy Walker for his major contribution to data preparation and his expert statistical input. This work was supported by the University of Edinburgh. VS is an Academic Clinical Lecturer funded by the National Institute of Health Research (NIHR). The views expressed are those of the authors and not necessarily those of the NHS, the NIHR or the ISD.
Introduction Incidence rates of cutaneous malignant melanoma and non-melanoma skin cancer (NMSC) in Canada have been steadily increasing between 1986 and 2010 . The estimated age standardized incidence rate for melanoma in 2017 was 18.5 cases per 100,000 (7300 cases)  and 198.4 for NMSC (78,300 cases) in 2015 . Melanoma is the most deadly form of skin cancer, and has become one of the most common cancers among young adults in Canada, particularly for females . Of NMSC cases, approximately 77% are basal cell carcinoma (BCC) and 23% are squamous cell carcinoma (SCC) . Although rarely fatal, the high incidence of NMSC represents a significant burden of disease in terms of morbidity, quality of life, social impact, and health care costs . There is consistent epidemiologic evidence that indoor tanning causes melanoma and non-melanoma skin cancer (NMSC) and in 2012 the International Agency for Research on Cancer (IARC) classified artificial sources of ultraviolet radiation as carcinogenic (class 1) to humans . Indoor tanning is similar to sun exposure for ultraviolet B (UVB) radiation exposure, but is 10–15 times stronger than sun exposure for ultraviolet A (UVA) radiation . With longer wavelengths than UVB radiation, UVA rays penetrate more deeply into the skin than UVB, and can cause mutations in tumor suppressor Protease Inhibitor Cocktail or other oncogenes, both directly through DNA damage and indirectly through oxidative stress . Moreover, UVA has been shown to be relatively ineffective at inducing pigmentation changes that can attenuate the potentially damaging effects of future exposure to UVR, as UVB does . Additionally, indoor tanning devices have been shown to induce harmful burns, which an estimated two-thirds of users experience at least once . While indoor tanning devices in Europe are limited in intensity to an ultraviolet index of 12, Canada and the USA do not place restrictions on owners or users . In addition, there is some evidence that the risk of skin cancer associated with ever use of indoor tanning devices is greater in North America than in Europe , which could be a reflection of varying use patterns and device restrictions. Population attributable risks (PAR) for skin cancer associated with indoor tanning have previously been estimated for Europe [12,13], France , Australia , and the United States , but not for Canada. Two main limitations of these previous studies is that they did not restrict the studies included in the PAR estimates for ever use of indoor tanning devices to those with a relevant exposure distribution to their own population, and they included studies that did not control for confounding from exposure to solar UVR exposure. Therefore, not only does a Canadian estimate require an exposure distribution for Canada, but it also requires a relative risk estimate that is applicable to the types of devices and usage patterns which represent Canadian indoor tanning exposure. While Brazil and Australia have banned indoor tanning devices , Canada only restricts use to those over the age of 18 . In addition, indoor tanning users in Canada are required to wear protective glasses and all commercial equipment must display labels that detail the health risks of indoor tanning, including that it can cause cancer . However, minors can still use tanning devices with signed consent from a guardian, and restriction in terms of intensity, frequency, or duration of use are not mandated in Canada . Therefore, attributable burden estimates have important implications for policy and preventive initiatives aimed at reducing the burden of skin cancer in Canada. Thus, the objective of this study was to estimate the risk of skin cancer associated with the ever use of indoor tanning devices that is relevant to Canada and to quantify the proportion and number of skin cancer cases in Canada that could be attributed to indoor tanning in 2015. A secondary objective included exploring the extent to which PAR estimates varied by age, sex, and province.