Additional prognostic value of the BCT score in patients with ER+HER2- breast cancer receiving 21-gene assay–guided adjuvant treatments.

Abstract

548 Background: In early estrogen receptor (ER)+HER2- breast cancer, a 21-gene expression assay-guided decision-making for adjuvant treatments has been widely utilized as a standard-of-care. The GenesWell BCT is a multigene assay that is designed to predict the risk of distant recurrence (DR) in patients with ER+HER2- breast cancer. This assay consists of nine genes, which are used to generate a risk score that can help guide treatment decisions. We addressed an additional value of the GenesWell Breast Cancer Test (BCT) score using the cohort of ER+HER2- breast cancer patients receiving a 21-gene assay-guided adjuvant treatments, focusing the chemotherapy untreated subset with low 21-gene recurrence score (RS). Methods: This multicentre, observational follow-up study was done in 4 academic institutions in South Korea. Patients with ER+HER2- breast cancer who received RS-guided adjuvant treatments were enrolled. A total of 705 patients were included. Of these, the rate of women with node-positive disease was 21.6% (152/705), and the rate of women with younger than 50 years old was 61.4% (433/705). The BCT score was obtained using the specimens which were previously analyzed for RS. The primary endpoint was recurrence-free survival (RFS), and the secondary endpoint was distant recurrence-free survival (DRFS). Results: Among the 705 patients, the RS assigned 110 (15.6%) as high risk (≥26), whereas the BCT score assigned 239 (33.9%) as high risk (≥4). The agreement between two tests was noted in 494 (70.1%); concordances were made in 69 for high and in 425 for low, respectively. At a median follow up of 85 months, 80 had tumor recurrences, 38 had distant recurrences, and the 7-year RFS was 90.0% (95% CI, 87.6%-92.5%). In the 595 patients with low RS, 556 (93.4%) did not receive adjuvant chemotherapy. Within the 556 chemotherapy-untreated patients with low RS, the RFS differed significantly according to the BCT score ( p= .014); the 7-year RFS was 92.9% in the BCT-low, while it was 85.7% in the BCT-high. Within the group, the BCT score was demonstrated as an independent prognostic factor for both RFS and DRFS adjustment of tumor size, nodal stage, and histologic grade. In addition, the RFS of the low-BCT score group was superior to that of the high-BCT group in either women younger than 50 years of age with an RS of 21 to 25 or all women with an RS of 21 to 25. Conclusions: We found that the BCT score was useful in stratifying the risk of relapse in chemotherapy-untreated patients with a low recurrence score (RS). This indicates that the BCT score could provide additional clinical value in identifying patients with a long-term risk of relapse, particularly in young women with an RS of 21 to 25.