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Contraception. 1997 Apr;55(4):197-203.

Modification of oral contraceptive relationships on breast cancer risk by selected factors among younger women.

Author information

1
Environmental Epidemiology Branch, National Cancer Institute, Bethesda, MD 20892, USA. brinton@epndce.nci.nih.gov

Abstract

In a case-control study of 1647 breast cancer cases and 1501 population controls under 45 years of age, potential modifying effects of other risk factors on the relationship of oral contraceptives to breast cancer were examined. Among the total series of study subjects, the relationship of extended pill usage was greater in non-white than white women. Oral contraceptive associations, however, did not appear to be substantially modified by other risk factors, including parity, body size, or family history of breast cancer (apart from a somewhat enhanced relationship among subjects who reported a sister with breast cancer. Further, oral contraceptive relationships did not vary by a history of benign breast disease, although the majority of subjects began pill usage prior to the development of benign breast disease. Among the women under the age of 35, in whom oral contraceptive relationships were heightened (over a twofold excess risk for use of 5 years or longer), pill relationships were less modified by race than in the total series. Although among these younger subjects there was no effect of pill usage in heavy women, and an enhanced relationship among heavier consumers of alcoholic beverages, these interactive effects were not statistically significant. The findings of this study generally support no substantial variation in oral contraceptive relationships by other breast cancer risk factors, although some further attention might be warranted regarding possible modifying effects of race, body size, type of relative with breast cancer, and alcohol consumption.

PIP:

To assess the possible interactive effects of oral contraceptives (OCs) with selected breast cancer risk factors, a case-control study involving US women diagnosed with breast cancer before 45 years of age was conducted. All incident cases of breast cancer diagnosed among younger women during 1990-92 in Atlanta, Georgia, Seattle/Puget Sound, Washington, and five counties of central New Jersey were eligible. Controls were identified through random-digit dialing. The final sample consisted of 1647 cases and 1501 controls. Ever-use of OCs for 6 months or more was associated with a slightly elevated breast cancer risk (relative risk (RR), 1.3; 95% confidence interval (CI), 1.1-1.5), with a stronger association for women whose breast cancer was diagnosed prior to age 35 years (RR, 1.8; 95% CI, 1.2-2.7). Among women under age 35 years, the risk was highest among women who had used OCs for 5 or more years and for those who used them within the past 5 years. In general, study findings did not support extensive variations in the risk associated with OC use across most risk factors. However, there were some noteworthy variations. At ages 35-44 years, long-term OC use exerted stronger effects in African-American women (RR, 1.5; 95% CI, 0.9-2.6) and other non-White women (RR, 2.8; 95% CI, 1.2-6.6) than among White women (RR, 1.0; 95% CI, 0.8-1.3). Although there was no interaction between OC use and a family history of breast cancer, OC use by a woman with a sister with breast cancer elevated the cancer risk. Body size was inversely associated with breast cancer risk in OC users, while weekly consumption of 7 or more alcoholic drinks slightly raised this risk.

PMID:
9179450
[Indexed for MEDLINE]

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