Low-dose oral contraceptives: Protective effect on ovarian cancer risk

Low-dose oral contraceptive (OC) formulations containing 35 mug or less eth inyl estradiol have preferably been prescribed in the last decade, however, few data exist on its relation to ovarian cancer risk. We determined the e ffects of low-dose OC on the risk of ovarian cancer in a population-based c ase-control study, including 282 patients ages 20-75 years at diagnosis of incident primary invasive ovarian cancer or borderline tumour between 1993- 1996 and 533 control subjects individually matched by age and study area to each case. Analysis excluded women who had undergone a bilateral ovariecto my or had a previous diagnosis of either ovarian cancer or borderline tumou r. The association of OC use by ethinyl estradiol dose and ovarian cancer r isk was assessed by odds ratios (OR), adjusting simultaneously for the othe r OC types and determinants of ovarian cancer risk. Ovarian cancer risk was significantly reduced by 52% for ever use of any type of OC. The reduction in risk was 7% per year of use (OR = 0.93, 95% confidence interval [CI] = 0.90-0.96) and was more evident in first-use subjects younger than 25 years . Risk reduction for ovarian cancer was substantial for use of low-dose OC, the odds ratios being 0.86 (95% CI = 0.77-0.94), 0.91 (95% CI = 0.83-1.00) , and 0.95 (95% CI = 0.91-0.99) per year of using OC containing < 35 mug, 3 5-< 50 mug, and greater than or equal to 50 mug ethinyl estradiol, respecti vely. Our study provides evidence that low-dose oral contraceptives confer substantial protection against the development of ovarian cancer. (C) 2001 Wiley-Liss, Inc.