Abstract
Data on adjuvant chemotherapy (CT) benefit in ER + HER2‒ early-stage breast cancer (EBC) patients with Recurrence Score (RS) 26-30 are limited. This real-world study evaluated the relationships between the RS, adjuvant treatments, and outcomes in 534 RS 26-30 patients tested through Clalit Health Services (N0: n = 394, 49% CT-treated; N1mi/N1: n = 140, 62% CT-treated). The CT-treated and untreated groups were imbalanced (more high-risk clinicopathologic characteristics in CT-treated patients). With median follow-up of 8 years, Kaplan-Meier estimates for overall survival (OS), distant recurrence-free survival (DRFS), and BC-specific mortality (BCSM) were not significantly different between CT-treated and untreated N0 patients. Seven-year rates (95% CI) in CT-treated vs untreated: OS, 97.9% (94.4-99.2%) vs 97.9% (94.6-99.2%); DRFS, 91.5% (86.6-94.7%) vs 91.2% (86.0-94.6%); BCSM, 0.5% (0.1-3.7%) vs 1.6% (0.5-4.7%). For N1mi/N1 patients, OS/DRFS did not differ significantly between treatment groups; whereas BCSM did (1.3% [0.2-8.6%] vs 6.2% [2.0-17.7%] for CT-treated and untreated patients, respectively, p = 0.024).