Hormone replacement therapy and breast cancer risk in a nationally representative cohort

Background: The relative risk of breast cancer associated with the use of postmenopausal hormone replacement therapy (HRT) continues to be debated. We used a nationally representative cohort to study the issue. Methods: This analysis utilized data from the NHANES I Epidemiologic Follow-up Study. Subjects were interviewed in 1971 through 1974 and four waves of follow-up interviews were conducted through 1992. Survival analysis of 5761 postmenopausal women provided estimates of the relative risk of breast cancer in users of HRT when compared with non-users, controlling for potential confounders. Results: There were 219 incident cases of breast cancer in 73,253 person-years of follow-up. The incidence rate was 326 per 100,000 person-years in women who had never used HRT and 255 per 100,000 in women who had ever used HRT. There was no statistically significant association between the HRT use and subsequent development of breast cancer: relative risk (RR) = 0.8, 95% confidence interval 0.6, 1.1. There was no trend in RR by length of HRT use: less than 3 years HRT use, RR = 0.9; 3 to 9 years , RR = 0.5; 10 or more years, RR = 0.8. Conclusions: This study, based on a nationally representative cohort followed for up to 22 years, failed to find an increased risk of breast cancer associated with the use of HRT. It provides further evidence that if there is an increased risk of breast cancer associated with HRT use, this risk is small.