MENOPAUSAL ESTROGEN AND ESTROGEN-PROGESTIN REPLACEMENT THERAPY AND RISK OF BREAST-CANCER (UNITED-STATES)

This study examines the relationship between menopausal estrogen and e strogen-progestin replacement therapy and risk of breast cancer, focus ing on whether associations differ according to whether the tumors are in situ or invasive. Data are from a prospective study conducted 1980 -89 on 49,017 selected participants in the Breast Cancer Detection Dem onstration Project, a five-year screening program conducted between 19 73 and 1980 in the United States. Overall, the rate ratio for estrogen -only use compared with no-hormone use was 1.0, and that for the estro gen-progestin combination was 1.2 (95 percent confidence interval [CI] = 1.0-1.6). However, the associations differed according to whether t he tumors were in situ or invasive. The rate ratios of in situ breast cancer associated with use of estrogens alone and the combination regi men were 1.4 (CI = 1.0-2.0) and 2.3 (CI = 1.3-3.9), respectively. Dura tion of estrogen-only use also was associated with risk of in situ tum ors, with users for 10 or more years at twice the risk of nonusers (P- value for trend test = 0.02). Duration of use was not associated with risk of invasive cancer. Our results are consistent with the hypothesi s that hormone replacement therapy is related to earlier-stage breast cancer; however, the possibility that the results reflect increased br east cancer surveillance among those taking hormones cannot be ruled o ut.