The effects of hormone replacement therapy on postmenopausal breast cancer biology and survival.

BACKGROUND The goal of this study was to compare the characteristics of breast cancers and survival rates in HRT users versus nonusers. METHODS Data were analyzed for 1055 patients > or = 50 years of age who had definitive therapy for breast cancer from 1994 through 2002. RESULTS There were 471 (45%) HRT users. The median age at diagnosis was 61.0 years for HRT users and 68.0 years for HRT nonusers (P < .001). HRT users more often had tumors that were <1 cm (P = .007), node negative (P = .033), and grade I (P = .016). HRT users had a decreased risk of death versus nonusers (hazard ratio = .438, 95% confidence limit = .263 to .729, P = .002). CONCLUSIONS HRT users developed breast cancer at a younger age than nonusers; HRT use was associated with the development of biologically more favorable cancers than those that developed in nonusers; and overall and disease-free survival rates were higher in HRT users than nonusers.