Oral contraceptive use and risk of breast cancer: a meta-analysis of prospective cohort studies

It has been suggested that taking oral contraceptives (OCs) may increase breast cancer incidence. However, data in this regard are inconsistent. We performed this meta-analysis to estimate the association between OC use and breast cancer risk.

Prospective cohort studies on OC use and breast cancer risk were identified by searching databases from the period 1960 to 2012. Results from individual studies were synthetically combined using STATA 11 software.

A total of 13 prospective cohort studies were included in our meta-analysis, involving 11,722 cases and 859,894 participants. The combined relative risk (RR) of breast cancer for ever- compared with never-OC users was 1.08 (95% confidence interval [CI]: 0.99-1.17). Dose-response analysis based on five eligible studies showed that every ten-years' increment of OC use was associated with a significant 14% (95% CI: 1.05-1.23) rise in breast cancer risk. Little evidence of publication bias was found.

This meta-analysis provides evidence of a non-significant increase in breast cancer risk associated with ever OC use, but the risk for long-term OC users is significantly greater. However, the latter finding is based on only a limited number of studies.