Impact of the 21-gene expression assay on treatment decisions and clinical outcomes in breast cancer with one to three positive lymph nodes.

Abstract

To assess the practice patterns of the recurrence score (RS) based on the 21-gene expression assay on adjuvant chemotherapy recommendations and survival outcomes in estrogen receptor-positive (ER+)/HER2- breast cancer (BC) with one to three positive lymph nodes (N1). We included patients with T1-2N1M0 and ER+/HER2- BC diagnosed between 2010 and 2015 in the Surveillance, Epidemiology, and End Results Oncotype DX Database. Breast cancer-specific survival (BCSS) and overall survival (OS) were assessed. We included 35,137 patients in this study. There were 21.2% of patients who had RS testing in 2010, which was significantly increased to 36.8% in 2015 (P < 0.001). Performance of the 21-gene testing was associated with older age, lower tumor grade, T1 stage, lower number of positive lymph nodes, and progesterone receptor-positive disease (all P < 0.05). In those without 21-gene testing, age was the main factor significantly related to the receipt of chemotherapy, whereas RS was the main factor significantly related to chemotherapy receipt in those with 21-gene testing. The probability of chemotherapy receipt in those without 21-gene testing was 64.1% and was decreased to 30.8% in those with 21-gene testing. On multivariate prognostic analysis, the performance of 21-gene testing was associated with better BCSS (P < 0.001) and OS (P < 0.001) compared with those without 21-gene testing. Similar results were found after propensity score matching. The 21-gene expression assay is frequently and increasingly used for chemotherapy decision-making in ER+/HER2- BC with N1 disease. Performance of the 21-gene testing is associated with improved survival outcomes. Our study supports the routine use of 21-gene testing in the clinical practice of this population.