Breast Cancer There is a large volume of conﬂicting literature on the relationship between OC use and breast cancer (173). No increase in overall risk is found from OC use, but some studies found that risk may increase in women who used OCs before their first term pregnancy, used OCs for many years, are nulligravid, are young at the time of diagnosis, or continue using OCs in their 40s. A meta-analysis of 54 studies of breast cancer and hormonal contraceptive use reanalyzed data on 53,297 women with breast cancer and 100,239 controls from 25 countries, representing about 90% of the epidemiologic data available worldwide at that time (174). Current use of OCs was associated with a very small, but statistically stable 24% increased relative risk (1.24; 95% CI, 1.15–1.33). The risk fell rapidly after discontinuation, to 16% 1 to 4 years after stopping and to 7% 5 to 9 years after stopping. Risk disappeared 10 years after cessation (relative risk, 1.01; 95% CI, 0.96–1.05). Results did not differ in any important way by ethnic group, reproductive history, or family history. Since the meta-analysis was published, subsequent studies found no increased risk. A case-control study of 4,575 women with breast cancer and 4,682 controls aged 35 to 64 years living in five cities in the United States concluded that breast cancer risk was not increased for current or past users of OCs and did not increase with prolonged or with higher-estrogen OC use (175). Neither family history of breast cancer nor beginning use at a young age was associated with increased risk. A similar study in Sweden compared 3,016 women aged 50 to 74 years who had invasive breast cancer with 3,263 controls of the same
Health Benefits of Oral Contraceptives age. No relation was found between past use of OCs and breast cancer (176). Effect of hormone dose was explored in a 2008 US study of 1,469 women with breast cancer who were matched by race, age, and neighborhood to community controls. The investigators then administered questionnaires and performed BRCA1 and 2 testing. Subjects who began OC use during or after 1975 were considered to have used low-dose pills. “Low-dose” was not further defined. Neither OC use overall or “low-dose” OC use was associated with breast cancer risk, among the total group, or within any subset. Women with BRCA1 or 2 did not have higher rates of cancer whether they were OC users or were nonusers (177). The controversy over the association between breast cancer and OC use is likely to continue. The best information available is that there is little or no connection.