NSABP P-1 — Tamoxifen for the Prevention of Breast Cancer in High-Risk Women (Breast Cancer Prevention Trial)

Phase 3 · 1998 · Breast Cancer

Design

Randomized tamoxifen 20 mg daily vs placebo for 5 years in women at increased risk.

Population

Women at high risk of breast cancer by the Gail model (age 60+, or younger with elevated risk).

Primary Endpoint

incidence of invasive breast cancer

Key Result

Tamoxifen cut invasive breast cancer incidence by roughly 49%, at the cost of increased endometrial cancer and thromboembolic events.

Guideline Impact

Basis for risk-reducing endocrine therapy in high-risk women