Oral Contraceptives and Cancer Risk

An initial analysis of an ongoing, multicenter case-control study indicates that women who have used oral contraceptives are approximately half as likely to develop ovarian and endometrial cancer as women who have never used them and that, despite previous concerns, contraceptive use does not appear to increase a woman's risk of breast cancer.

The study used population-based cancer registries in eight geographic regions across the United States to identify women 20-54 years of age with newly diagnosed breast, ovarian, or endometrial cancer. Controls were women of the same ages without known cancer, chosen from the same geographic areas by dialing randomly selected telephone numbers.

The relative risk of ovarian cancer for women who had used oral contraceptives for at least 1 month, as compared with women who had never used them, was 0.6 (95% confidence limits 0.4-0.9). The longer a woman had used oral contraceptives, the lower her risk of developing ovarian cancer. The protective effect of oral contraceptive use persisted more than 10 years after pill use was discontinued.

The relative risk of ovarian cancer for women who had used oral contraceptives for at least 1 month, as compared with women who had never used them, was 0.6 (95% confidence limits 0.4-0.9). The longer a woman had used oral contraceptives, the lower her risk of developing ovarian cancer. The protective effect of oral contraceptive use persisted more than 10 years after pill use was discontinued.

The relative risk of endometrial cancer for women who had used combined oral contraceptives containing both an estrogen and a progestin was 0.5 (95% confidence limits 0.4-0.8). By contrast, women who had used sequential oral contraceptives (estrogen and progestin components taken at different times of the month) appeared to have an increased risk of endometrial cancer. The protective effects of combined oral contraceptives against endometrial cancer appeared to be restricted to women who had used them for 1 year or longer and was concentrated in nulliparous women.

For breast cancer, women who had used oral contraceptives had a relative risk of 0.9 (95% confidence limits 0.8-1.2) compared with women who had never used them. There was no evidence that long-term oral contraceptive use of more than 10 years or oral contraceptive use that began 16 or more years ago, shortly after oral contraceptives were introduced in this country, increased the risk of breast cancer. Furthermore, there was no indication of any increased risk of breast cancer due to oral contraceptive use for high-risk women such as those with family histories of breast cancer or with previous biopsies for benign breast disease. Similarly, there was no evidence of an increased risk of breast cancer for women who used oral contraceptives before their first pregnancy. Reported by M Child, MD, F Vellios, MD, Emory University, Atlanta; JW Meigs, MD, WD Thompson, PhD, C White, MBBS, Yale University School of Medicine, New Haven; M Swanson, PhD, Michigan Cancer Foundation, Detroit; M Corder, MD, E Smith, PhD, University of Iowa College of Medicine, Iowa City; C Key, MD, D Pathak, PhD, New Mexico Tumor Registry, Albuquerque; D Austin, MD, California Dept for Health Svc, Emeryville; D Thomas, MD, Fred Hutchinson Cancer Research Center, Seattle; J Lyon, MD, D West, PhD, Utah Cancer Registry, Salt Lake City; L Burnett, MD, Vanderbilt University Hospital, F Gorstein, MD, Vanderbilt Medical Center, Nashville; A Paris, MD, West Plains Memorial Hospital, West Plains, R McDivitt, MD, Jewish Hospital of St. Louis, W Bauer, MD, D Gersell, MD, Washington University School of Medicine, St. Louis, Missouri; S Robboy, MD, Massachusetts General Hospital, Boston; R Hoover, MD, National Cancer Institute, JJ Schlesselman, PhD, Uniform Svcs University of the Health Sciences, B Stadel, MD, National Institutes of Child Health and Human Development, Bethesda; D Schottenfeld, MD, Memorial Sloane-Kettering Cancer Center, New York; W Christopherson, MD, University of Louisville Health Sciences Center, Kentucky; R Kurman, MD, Georgetown University School of Medicine, Washington, D.C.; Center for Population Research, National Institute of Child Health and Human Development, Carcinogenesis Extramural Program, National Cancer Institute; Family Planning Evaluation Div, Center for Health Promotion and Education, CDC.

Editorial Note

Editorial Note: The Cancer and Steroid Hormone Study is a collaborative effort of the National Cancer Institute and eight Surveillance, Epidemiology, and End Results (SEER) Centers of the Institute, the National Institute of Child Health and Human Development, and the Centers for Disease Control. It is specifically designed to clarify the association between oral contraceptive use and breast, endometrial, and ovarian cancer.

Methodologic biases are unlikely to account for the study's findings. Selection bias was minimized by attempting to enroll all women from the eight geographic areas who have newly diagnosed breast, endometrial, or ovarian cancer and by selecting controls at random from the same areas. Accurate histories of oral contraceptive use were facilitated by a book containing photographs of all oral contraceptives ever marketed in the United States and by a calendar with which the women could relate periods of contraceptive use to reproductive histories and other life events (1). Because of the widespread use of oral contraceptives and the common occurrence of endometrial and ovarian cancer, the protective effects of oral contraceptives against these tumors could have a large public health impact. The reduced risk of cancer among women who have used oral contraceptives would result in the prevention of over 1,700 cases of ovarian cancer and over 2,000 cases of endometrial cancer in the United States each year.

References

1. Rosenberg MJ, Layde PM, Ory HW, Strauss LT, Rooks JB, Rubin GL. Agreement between women's histories of oral contraceptive use and physician records. Int J Epidemiol (In Press).

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