THE ROLE OF HORMONE REPLACEMENT THERAPY IN THE RISK FOR BREAST-CANCERAND TOTAL MORTALITY IN WOMEN WITH A FAMILY HISTORY OF BREAST-CANCER

Background: The risks and benefits of hormone replacement therapy (HRT ) are of considerable interest and importance, especially in terms of whether they differ among subsets of women. Objective: To determine wh ether HRT is associated with increased risks for breast cancer and tot al mortality in women with a family history of breast cancer. Design: Prospective cohort study. Setting: Population-based sample of midweste rn post-menopausal women enrolled in an observational study of risk fa ctors for cancer. Participants: Random sample of 41 837 female Iowa re sidents 55 to 69 years of age. Measurements: Incidence rates of and re lative risks for breast cancer (n = 1085) and total mortality (n = 203 5) th rough 8 years of follow-up were calculated by using data from th e State Health Registry of Iowa and the National Death Index. Results: A family history of breast cancer was reported by 12.2% of the cohort at risk. Among women with a family history of breast cancer, those wh o currently used HRT and had done so for at least 5 years developed br east cancer at an age-adjusted annual rate of 61 cases per 10 000 pers on-years (95% CI, 28 to 94 cases); this rate was not statistically sig nificantly higher than the rate in women who had never used HRT (46 ca ses per 10 000 person-years ICI, 36 to 55 cases]). Among women with a family history, those who used HRT had a significantly lower risk for total mortality than did women who had never used HRT (relative risk, 0.67 [CI, 0.51 to 0.89]), including total cancer-related mortality (re lative risk, 0.75 [CI, 0.50 to 1.12]). The age-adjusted annual mortali ty rate for women using HRT for at least 5 years was 46 deaths per 10 000 person-years (CI, 19 to 74 deaths); this is roughly half the rate seen in women who had never used HRT (80 deaths per In 000 person-year s [CI, 69 to 92 deaths]). Conclusions: These data suggest that HRT use in women with a family history of breast cancer is not associated wit h a significantly increased incidence of breast cancer but is associat ed with a significantly reduced total mortality rate.