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The incidence of ovarian cancer increases with age. Oral contraceptives (OCs) lower risk for ovarian cancer, but how long does this benefit persist after OC use is discontinued? To investigate this question, researchers combined individual data from 45 observational studies of risk factors for ovarian cancer; they built a large case-control database that represents 23,257 women with ovarian cancer and 87,303 women without ovarian cancer.
Thirty-one percent of cases and 37% of controls had ever used OCs. Compared with never-users of OCs, ever-users had an overall relative risk for ovarian cancer of 0.73. Risk reduction was tied to duration of OC use; 15 years of use lowered relative risk by half. Those who had ceased OC use within the past de…