The 21-gene recurrence score in node-positive, hormone receptor-positive, HER2-negative breast cancer: a cautionary tale from an NCDB analysis.

The 21-gene recurrence score assay (RS) has not been prospectively validated to predict adjuvant chemotherapy benefit in hormone receptor-positive (HR+), HER2-negative (HER2-), node-positive breast cancer patients. Nevertheless, de-escalation based on RS has been demonstrated and partially advocated by retrospective data. The purpose of this study was to identify subgroups of node-positive patients with low to intermediate RS who still benefit from adjuvant chemotherapy. The National Cancer Database was used to identify 28,591 women with stage I-III, T1-T3, N1, HR+, HER2- breast cancer and a RS ≤ 25 between 2010 and 2016. Univariate and multivariate analyses were used to identify variables correlating with chemotherapy use and 5-year survival. Subgroup analysis was performed to discern patients in whom the use of adjuvant chemotherapy correlated with better survival. A 35% decline in chemotherapy use was observed from 2010 to 2016. Patients with younger age, higher RS, larger tumors and more positive lymph nodes, and those treated by mastectomy, axillary lymph node dissection and radiation, were more likely to receive chemotherapy. Chemotherapy use was associated with an improved 5-year survival (HR = 1.63, 95% CI 1.28-2.07). Upon subgroup analysis, this association was lost in patients > 70 years and those with a RS ≤ 11, while patients ≤ 70 with a RS of 12-25 treated with chemotherapy had an absolute 5-year survival advantage of 3.0% (HR = 1.91, 95% CI 1.42-2.57). Clinicians should be cautious when considering omission of adjuvant chemotherapy in patients ≤ 70 years, with HR+, HER2-, N1 tumors and a RS 12-25, at least until the results of the anticipated RxPONDER trial become available.