Ten prospective studies, 25 case-control studies with population control, and 14 case-control studies with hospital controls were included (52,925 cases and 99,018 controls).
For women currently taking COC, and for 10 years after stopping, there was a small increase in the RR of breast cancer.
Current users, RR 1.24 (95% confidence interval, CI: 1.15, 1.33, 2p>0.00001); 1 to 4 years after stopping COC, RR 1.16 (95% CI: 1.08, 1.23, 2p=0.00001); 5 to 9 years after stopping COC, RR 1.07 (95% CI: 1.02, 1.13, 2p=0.009).
There was no significant excess risk of having breast cancer diagnosed 10 or more years after stopping COC: RR 1.0. (95% CI: 0.96, 1.05, non significant). The cancers diagnosed in women who had used COC were less advanced clinically than those diagnosed in never-users. The RR of tumours that had spread beyond the breast compared to localised tumours, in ever-users compared to never-users, was 0.88 (95% CI: 0.81, 0.95, 2p=0.002).