Recent oral contraceptive use and risk of breast cancer (United States).

We examined the association between recent oral contraceptive (OC) use and the risk of breast cancer in data from a large population-based case-control study in the United States. Cases (n = 6,751) were women less than 75 years old who had breast cancer identified from statewide tumor registries in Wisconsin, Massachusetts, Maine, and New Hampshire. Controls (n = 9,311) were selected randomly from lists of licensed drivers (if aged under 65 years) and from lists of Medicare beneficiaries (if aged 65 through 74 years). Information on OC use, reproductive experiences, and family and medical history was obtained by telephone interview. After adjustment for parity, age at first delivery, and other risk factors, women who had ever used OCs were at similar risk of breast cancer as never-users (relative risk [RR] = 1.1, 95 percent confidence interval [CI] = 1.0-1.2). Total duration of use also was not related to risk. There was a suggestion that more recent use was associated with an increased risk of breast cancer; use less than two years ago was associated with an RR of 1.3 (CI = 0.9-1.9). However, only among women aged 35 to 45 years at diagnosis was the increase in risk among recent users statistically significantly elevated (RR = 2.0, CI = 1.1-3.9). Use prior to the first pregnancy or among nulliparous women was not associated with increased risk. Among recent users of OCs, the risk associated with use was greatest among non-obese women, e.g., among women with body mass index (kg/m2) less than 20.4, RR = 1.7, CI = 1.1-2.8. While these results suggest that, in general, breast cancer risk is not increased substantially among women who have used OCs, they also are consistent with a slight increased risk among subgroups of recent users.