Background: Hormonal contraceptives and hormone replacement therapies are classified as carcinogenic to humans (group 1) by the International Agency for Research on Cancer. We sought to estimate the proportion and total number of cancers attributable to the use of oral contraceptives and hormone therapy in Alberta in 2012.
Methods: Population attributable risks were used to estimate the proportion of attributable cases for each associated cancer site. Relative risk estimates were obtained from the most relevant and recent epidemiologic literature. Prevalences of the use of oral contraceptives and hormone therapy in Alberta were collected from Alberta's Tomorrow Project. Specific cancer incidence data were obtained from the Alberta Cancer Registry for the year 2012.
Results: Overall, 6.3% of breast cancers (n = 135) diagnosed in Alberta in 2012 were estimated to be attributable to the use of oral contraceptives, and the exposure potentially prevented about 57.3% of endometrial cancers (n = 276) and 29.1% of ovarian cancers (n = 52). About 15.5% of breast cancers (n = 258) and 8.9% of ovarian cancers (n = 13) were estimated to be attributable to the use of hormone therapy, whereas 11.3% of endometrial cancers (n = 48) were possibly prevented by the exposure.
Interpretation: Based on our estimates, oral contraceptive use resulted in a net protective effect among the cancer sites studied, thus reducing the cancer burden in Alberta in 2012. The use of hormone therapy was estimated to increase the cancer burden in the province, therefore the risk and benefit of hormone therapy should be carefully considered before use.