Effectiveness of adjuvant tamoxifen therapy among older women with early stage breast cancer.

To investigate the effectiveness of adjuvant tamoxifen in older women with early-stage breast cancer. Between 1997 and 1999, women > or = 65 years old at diagnosis with stage I-IIIa breast cancer were recruited from four geographic regions of the United States and followed prospectively for 5 years after diagnosis. Data sources included tumor registries, medical records review, and telephone interviews. The primary end points were breast cancer-specific and overall survival ascertained by matching identifying data with the National Death Index and Social Security Administration master death file. Tamoxifen prescription was operationalized as tamoxifen prescribed by 6 months after diagnosis. Survival analysis was undertaken using Kaplan-Meier curves and Cox proportional hazards modeling. We studied 689 women whose average age was 74.2 years at diagnosis (SD = 6.3, range 65-96 years). The median follow-up was 67 months (range 3.5-88 months). Of the 689 patients, 519 (76%) were prescribed tamoxifen. The 5-year breast cancer-specific survival was 93% (95% CI = 90-95) and 89% (95% CI = 83-94) for the ever tamoxifen and never tamoxifen groups, respectively. The ratio of adjusted breast cancer mortality hazards was 0.61 (95% CI = 0.31-1.12) for the ever tamoxifen group versus the never tamoxifen group. Similarly, the 5-year overall survival was 81% (95% CI = 76-85) and 70% (95% CI = 61-78) for the ever tamoxifen and never tamoxifen groups, respectively, with an adjusted hazard ratio of 0.53 (95% CI = 0.37-0.77). Adjuvant tamoxifen is associated with improvement in 5-year breast cancer-specific and overall survival in older women with early-stage breast cancer.