BREAST-CANCER RISK AMONG WOMEN UNDER 55 YEARS OF AGE BY JOINT EFFECTSOF USAGE OF ORAL-CONTRACEPTIVES AND HORMONE REPLACEMENT THERAPY

Objective: To assess effects on breast cancer risk of exposure to both oral contraceptives and menopausal hormones, an increasingly common e xposure. Design: A case-control study of breast cancer among women und er the age of 55 years in Atlanta, GA involving 1,031 cases and 919 po pulation controls was conducted. Results: Ever use of oral contracepti ves was associated with a relative risk of 1.1 (95% 0.9-1.4), whereas the relative risk for hormone replacement therapy was 0.9 (95% CI 0.7- 1.2). Seventeen percent of the cases versus 19% of the population cont rols reported exposure to both agents, resulting in a relative risk of 1.0 (95% CI 0.7-1.4) relative to those unexposed to either preparatio n. Although there was little variation in risk associated with joint e ffects by either age or race, there were statistically nonsignificant elevations in risk for this exposure among women who had experienced a natural menopause (relative risk = 2.0, 95% CI 0.7-5.6), were relativ ely thin (relative risk = 1.5, 0.8-3.0), or who had a first degree rel ative with breast cancer (relative risk = 2.0, 0.6-7.0), When joint ef fects of longer term use of both agents were considered, subjects who reported use of oral contraceptives for 10 or more years and hormone r eplacement for 3 or more years had a relative risk of 3.2 (95% CI 1.4- 7.4) compared with nonusers of either preparation. Conclusions: Althou gh our results must be cautiously interpreted given small numbers with in subgroups, they raise concern and emphasize the need for further ev aluation on breast cancer risk of the increasingly common exposure to both oral contraceptives and hormone replacement therapy. (Menopause 1 998;5:145-151. (C) 1998, The North American Menopause Society.).