comparison with other studies By contrast with most previous research , our study included women aged 15 - 49 years , most of whom will have been premenopausal . Thus , the periods of observation for ever users of hormonal contraceptives in this age group had a higher proportion of information relating to current or recent use than those for ever users in a study recruiting older women , because many would have stopped using hormonal contraception many years previously . The Collaborative Group on Epidemiological Studies of Ovarian Cancer 's reanalysis of oral contraception data from 45 studies included women who were generally older than our cohort ( mean age of diagnosis of ovarian cancer was 56 years , with only 18 % of tumours diagnosed in women younger than 45 years ) . 4 The overall relative risk between ever and never users was 0.73 ( 95 % confidence interval 0.70 to 0.76 ) . The Collaborative Group 's analysis found that younger and premenopausal women seemed to have greater percentage reductions in risk of ovarian cancer per five years of oral contraceptive use . 4 However , after accounting for time since last use , no significant heterogeneity by menopausal status or age was seen , demonstrating that how recent a woman last used hormonal contraceptives was more important than the other two factors . Our slightly stronger reduced risk for any ovarian cancer among ever users of any hormonal contraception ( relative risk 0.66 ( 95 % confidence interval 0.58 to 0.76 ) ) was possibly due to 58 % of the total period of observation in ever users arising from current or recent use of combined oral contraceptives . Similar to the Collaborative Group 4 and other more recent investigations , [ 5][6][7][8][9 ] we found that the risk reductions among current users of any hormonal contraception got stronger with longer durations of use and persisted for a number of years after stopping use . The apparent loss of protection 10 years after stopping hormonal contraception could be due to the loss of biological effect ( assuming a causal association exists ) , or reduced statistical power to continue to observe a significant reduction due to the relatively small periods of observation ( 7 % of total person years for ever use ) .