Introduction Solar ultraviolet radiation (UVR) has potential protective, and confirmed detrimental effects on cancer risk. Several studies have examined recreational sun exposure in relation to breast cancer risk, and a recent meta-analysis found that moderate sun exposure (1–2 hrs/day) was associated with a decreased risk of breast cancer. Only one previous study in Canada has investigated UVR and breast cancer risk in an occupational setting.

Objectives The primary objective is to investigate the relationship between occupational solar UVR and breast cancer risk in Canada to inform on the dose-response relationship at the high end of the solar UVR spectrum.

Methods Questionnaire data from the Canadian Partnership for Tomorrow’s Health (CanPath) will be utilized for participants in Ontario, Quebec, and Alberta. Information on sun exposure, longest job held, and breast cancer risk factors were obtained at baseline. Cancer outcomes have been ascertained via linkage with provincial cancer registries. A case-cohort approach was employed to facilitate job coding. Jobs codes were linked to a job exposure matrix (SUNJEM) to assign exposure. Breast cancer risk estimates (hazard ratios [HR]) and 95% confidence intervals (CI) will be estimated using a weighted Cox proportional hazard’s regression with Prentice weights, controlling for potential confounders.

Results Preliminary results are available from the Ontario cohort, the analyses of additional cohorts are currently underway. From the underlying Ontario cohort 1,213 breast cancer cases met eligibility criteria. In the random sample of 2,500 women selected for the sub-cohort, the prevalence of occupational exposure (>2 hrs/day) to solar UVR was less than 2%. Preliminary HRs [0.995 (95%CI 0.684, 1.448)] suggest that occupational UVR does not have a protective or detrimental effect on the risk of breast cancer for Canadian women.

Conclusion This will be the second study to examine the relationship between occupational sun exposure and breast cancer risk in Canada, and the first to examine the dose-response relationship.