Hazard of Breast Cancer-Specific Mortality among Women with Estrogen Receptor-Positive Breast Cancer after Five Years from Diagnosis: Implication for Extended Endocrine Therapy

Purpose: More than half of the patients with estrogen receptor (ER)-positive breast cancers will relapse and die from breast cancer at 5–10 yr after diagnosis despite 5-yr endocrine therapy. Subpopulations of ER-positive patients at high risk of breast cancer-specific mortality (BCSM) at 5–10 yr are undetermined. Methods: Using the Surveillance, Epidemiology, and End-Results program (1990–2003), we analyzed the relative hazard ratio (HR) and absolute HR of BCSM and the cumulative 10-yr breast cancer-specific survival (BCSS) in 111,993 breast cancer patients, stratified by ER, age, and lymph node (LN), and adjusted for other prognostic factors. Results: At 5–10 yr after diagnosis, ER-positive patients had increased risk of BCSM [HR, 0.71; 95% confidence interval (CI), 0.66–0.76; ER-positive as reference] compared with ER-negative patients. Specifically, younger ER-positive patients (<40 yr) had a constant plateau of annual hazard rate, a higher hazard of BCSM (HR, 0.43; 95% CI, 0.35–0.52; ER-positive as re...