Weighing the Evidence on the Pill and Breast Cancer

Abstract

Three new studies have found some connection between oral contraceptive use and breast cancer among women younger than 45. None of the studies find an increased risk of breast cancer among the same subgroups of women, and their results are contradictory. Consequently, a committee advising the U.S. Food and Drug Administration concluded that "the existing data do not support a change in prescribing practices by physicians or in the use of oral contraceptives by women." One of the three studies, a U.S. hospital-based analysis of breast cancer patients, showed ever-users of the pill to have a statistically significant risk of breast cancer of 2.0 compared with never-users. The relative risk was elevated in virtually all duration-of-use categories. A significantly increased relative risk was also found among ever-users aged 30-34 and 35-39, among those who did not experience menarche until age 14 or older and among those who were parous. A new analysis of data from the U.S. population-based Cancer and Steroid Hormone Study found no increased risk among parous women or those who had used the pill for less than eight years. However, nulliparous women who had experienced menarche prior to age 13 and had used the pill for eight or more years did have a significantly increased relative risk. Most of the increased risk was confined to women who had begun pill use as teenagers; they had a relative risk of 5.6 compared with never-users.(ABSTRACT TRUNCATED AT 250 WORDS)3 recent research studies--all from well-established projects--have identified an association between oral contraceptive (OC) use and breast cancer in women under 45 years of age. In the 1st such study, a US hospital-based analysis of breast cancer patients, ever-users of OCs were found to have a relative risk of breast cancer of 2.0 compared with never-users. The risk was elevated in almost all duration-of-users categories. A significantly increased risk of breast cancer was also recorded among ever-users in the 30-39-year age groups, women who did not experience menarche until age 14 years or later, and parous women. The 2nd study, the US Cancer and Steroid Hormone (CASH) Study, found no increased risk of breast cancer among parous women or those who had used OCs for less than 8 years. However, nulliparous women who had experienced menarche prior to age 13 years were 2.7 times more likely to develop breast cancer before age 45 than were nulliparous women who had also experienced an early menarche but had never used the pill. Women with these characteristics who had used OCs for 12 or more years had a risk of breast cancer before 45 years of age that was 11.8 times that of never-users. Most of the increased risk was confined to women who began OC use as teenagers, however; they had a relative risk of 5.6 compared with never-users. The 3rd study, conducted by the UK Royal College of General Practitioners, found that ever-users aged 30-34 years at time of breast cancer diagnosis had a relative risk of breast cancer of 3.3 compared with never-users. Women of parity 1 had a relative risk of 5.9, but there was no increased risk of breast cancer among nulliparous women or those with more than 1 child. Although these studies contradict each other and are based largely on older OC formulations that contain higher doses of steroids than those currently marketed, the US Food and Drug Administration organized special hearings to evaluate their findings. The committee urged more research on the biology of the human breast as well as larger clinical studies of OC users, but concluded that the existing data do not support any changes in OC prescribing patterns or in the use of OCs.