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Oral Contraceptives & Breast Cancer
carcinogens (National Research Council, 1983, 1984). A modification of this approach that reflects the biology of the hormones found in oral contraceptives may be especially useful.
As mentioned earlier, breast cancer incidence rates increase steadily with age so that breast cancer is mainly a disease of the postmenopausal years (Table 1-7). A minority of breast cancer cases occur among women under the age of 45; therefore, most of the women who have had breast cancer since 1960 passed through their fertile years before oral contraceptives were widely used. Women now in their 40s, however, have used the pill more extensively and need answers to their questions about any possible interaction between the pill and breast cancer risk. In addition, if they use postmenopausal replacement hormones, questions about interaction with prior oral contraceptive use could become even more important.
When oral contraceptives were first approved for marketing by the FDA in 1960, they were known to be highly efficacious and thought by many not to have common, short-term, serious side effects. Little else was known about the more general effects of their use. With longer duration of use, an increasingly detailed picture of oral contraceptive risks and benefits is emerging (see Chapter 4). Today, practically the only important area to be resolved relates to breast cancer.
Overall, the pill has performed remarkably well as a relatively safe, effective, widely acceptable contraceptive (see Appendix E). Long-term follow-up has shown that oral contraceptive use can alter disease risk in pre- and perimenopausal women and that specific formulations modify these risks in different ways. The changes of greatest interest have been that certain types of cardiovascular disease have become more common and two reproductive cancers (i.e., ovarian and endometrial) have become less common. By developing different artificial hormones and reducing the amount of hormones in each tablet, some of the increased risk of cardiovascular disease observed in earlier, high-dose pills has been reduced without losing any of the cancer prevention benefits. Substantial gaps in data still exist, however. For example, although new progestins that are still making their way through the approval process in the United States have been widely used in Europe for a decade, there is no published body of epidemiological evidence on their influence on overall cardiovascular and cancer disease profiles. In addition, no postmenopausal women used oral contraceptives earlier in their reproductive lives for a period long enough to yield any information about systematic oral contraceptive influence on disease profiles. The lack of information on such influence applies not only to early but also to