Survival outcome of adjuvant chemotherapy and high 21-gene recurrence score in early-stage breast cancer

Among patients with early-stage breast cancer and a high 21-gene recurrence score (RS) >= 26, it remains unclear on whether those with RS 26-30 would benefit from chemotherapy with a comparable magnitude as those with RS > 30. In addition, RS > 30 as an independent prognostic factor for breast cancer-specific survival (BCSS) and overall survival (OS) compared to RS 26-30 also remains unclear. The Surveillance, Epidemiology, and End Results (SEER) database was queried for patients diagnosed between 2010 and 2013 with hormone receptor-positive, HER2-negative, and T1-2N0 breast cancer with a RS >= 26. Primary end points were OS and BCSS, evaluated by using Kaplan-Meier method, log-rank test, and Cox multivariable analysis. Subgroups of RS 26-30 and RS > 30 were examined using propensity score matching to address selection bias. Among 5054 patients who met the inclusion criteria, adjuvant chemotherapy was associated with improved OS (HR 0.66, 95% CI 0.53-0.83, P < .001) and BCSS (HR 0.61, 95% CI 0.45-0.83, P = .001). In the subgroup of 943 matched pairs of patients with RS 26-30, the addition of chemotherapy remained statistically significant (OS: HR 0.52, 95% CI 0.34-0.79, P = .003; BCSS: HR 0.42, 95% CI 0.22-0.81, P = .009). Among 1194 matched pairs who underwent adjuvant chemotherapy, those with RS > 30 had worse outcomes than others with RS 26-30 (OS: HR 1.68, 95% CI 1.17-2.42, P = .005; BCSS: HR 1.92, 95% CI 1.17-3.15, P = .01). Our study builds on prior literature using a population-based database to suggest the association of adjuvant chemotherapy with improved survival among those with RS 26-30 and worse mortality associated with RS > 30 compared to RS 26-30.