The performance of the 21-gene assay standard cutpoints of 18 and 31 in HR+, HER2- invasive breast cancer (BC), while waiting for TAILORx mid-range recurrence score results.

Abstract

537 Background: The Recurrence Score (RS) was shown in NSABP B-20 to predict chemotherapy (CT) benefit for RS ≥31 and no CT benefit for RS <18. The TAILORx results for RS <11 (NEJM 2015) reported excellent outcomes with no opportunity for CT to add additional benefit. As we await TAILORx results for RS 11-25, we characterized BC specific mortality (BCSM) for RS groups (cutoffs of 11, 18, 25, and 31) in the population-based SEER study of pts treated based on RS. Methods: RS results were provided to SEER registries per their methods (npj Breast Cancer 2016). Pts diagnosed (Jan 2004 - Dec 2012) with N0 HR+ HER2- negative BC, and no prior malignancy were eligible. BCSM estimates by CT use were computed using standard cutpoints of 18 and 31 and TAILORx cutpoints of 11 and 25. Results: Among 49,681 with a RS, 9,486 (19%) had RS <11, 17,988 (36%) had RS 11-17, 14,541 (29%) had RS 18-25, 3,805 (8%) had RS 26-30, and 3,861 (8%) had RS ≥31. Reported CT use and 5-y BCSM increased with increasing RS. For pts with both RS <11 and RS 11-17, CT use was uncommon and 5-y BCSM was low regardless of CT use. For pts with RS 18-25, CT use was more common and the 5-y BCSM was about 1% regardless of CT use. For pts with RS of 26-30 or ≥31, CT was common, and lower 5-y BCSM was observed with CT reported yes than with CT reported no or unknown. Conclusions: Pts in real-world clinical practice with RS <11, consistent with TAILORx, and pts with RS 11-17 have low 5-y BCSM with limited CT use, supporting hormonal therapy alone for pts with RS <18. The high end of the TAILORx mid-range (18-25) also showed good 5-y BCSM both with and without CT, highlighting the importance of the randomized results of TAILORx. [Table: see text]