Tamoxifen for the Prevention of Breast Cancer: Current Status of the National Surgical Adjuvant Breast and Bowel Project P-1 Study

Initial findings from the National Surgical Adjuvant Breast and Bowel Project Breast Cancer Prevention Trial (P-1) demonstrated that tamoxifen reduced the risk of estrogen receptor-positive tumors and osteoporotic fractures in women at increased risk for breast cancer. Side effects of varying clinical significance were observed. The trial was unblinded because of the positive results, and follow-up continued. This report updates our initial findings.

Women (n = 13,388) were randomly assigned to receive placebo or tamoxifen for 5 years. Rates of breast cancer and other events were compared by the use of risk ratios (RRs) and 95% confidence intervals (CIs). Estimates of the net benefit from 5 years of tamoxifen therapy were compared by age, race, and categories of predicted breast cancer risk. Statistical tests were two-sided.