How do oral contraceptives affect ovarian and endometrial cancer risk?
Studies have consistently shown that using OCs reduces the risk of ovarian cancer. In a 1992 analysis of 20 studies of OC use and ovarian cancer, researchers from Harvard Medical School found that the risk of ovarian cancer decreased with increasing duration of OC use. Results showed a 10 to 12 percent decrease in risk after 1 year of use, and approximately a 50 percent decrease after 5 years of use (5). Researchers have studied how the amount or type of hormones in OCs affects ovarian cancer risk reduction. One of the studies used in the Harvard analysis, the Cancer and Steroid Hormone Study (CASH), found that the reduction in ovarian cancer risk was the same regardless of the type or amount of estrogen or progestin in the pill (6). A more recent analysis of data from the CASH study, however, indicated that OC formulations with high levels of progestin reduced ovarian cancer risk more than preparations with low progestin levels (7). In another recent study, the Steroid Hormones and Re
