Abstract P6-13-03: Breast cancer-specific mortality (BCSM) in patients with node-positive (N+) breast cancer (BC) treated based on the 21-gene assay in clinical practice

Abstract

Abstract Introduction: The Recurrence Score® (RS) assay was shown in SWOG 8814 to predict chemotherapy (CT) benefit for patients (pts) with N+ BC and RS ≥31 but not RS <18. As we await the randomized RxPONDER results for RS 0-25, we characterized BCSM for RS groups (cutoffs of 11, 18, 25, and 31) in the large population-based SEER study of pts treated based on RS results. Methods: RS results were provided electronically to SEER registries per their linkage methods (Petkov npj Breast Cancer 2016). Eligible pts were diagnosed (Jan 2004 - Dec 2012) with N+ (micrometastases, 1-3 positive nodes), HR+, HER2-negative BC, and had no prior malignancy or multiple tumors. BCSM estimates by reported CT use were computed using standard cutpoints of 18 and 31 and TAILORx/RxPONDER cutpoints of 11 and 25, and should be interpreted cautiously given known under-reporting of CT use to SEER and lack of randomization. Results: Among 6,483 pts with RS results, 1,312 (20%) had RS <11, 2,478 (38%) had RS 11-17, 1,831 (28%) had RS 18-25, 432 (7%) had RS 26-30, and 430 (7%) had RS ≥31. There was a significant association between RS results and BCSM (p<0.001) without and with adjustment for age, tumor size, and grade. Reported CT use and 5-y BCSM increased with increasing RS result (Table). For pts with RS <11 and RS 11-17, CT use was reported in approximately a quarter of pts, 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 2%. For pts with RS of 26-30 or ≥31, CT was common, and higher 5-y BCSM was observed. 5-y BCSM, by RS Group and Reported CT Use CT reported as ‘No/Unknown’CT reported as ‘Yes’RS groupN (%)5-y BCSM (95% CI)N (%)5-y BCSM (95% CI)<111066 (81%)1.8% (0.7%, 4.6%)246 (19%)1.3% (0.3%, 5.3%)11-171869 (75%)0.5% (0.2%, 1.1%)609 (25%)2.3% (0.9%, 5.8%)18-251034 (56%)2.0% (1.0%, 3.9%)797 (44%)1.9% (0.8%, 4.5%)26-30144 (33%)7.7% (2.8%, 20.3%)288 (67%)4.0% (1.6%, 10.1%)≥3199 (23%)11.9% (5.3%, 25.6%)331 (77%)11.1% (6.9%, 17.6%) Conclusion: Reported CT use and 5-y BCSM in N+ BC increased with increasing RS results in “real-world” clinical practice. 5-y BCSM with RS <18 was less than 2% in pts with no or unknown CT use. 5-y BCSM in pts treated based on RS results appears to increase considerably with RS >25. Citation Format: Shak S, McCullough D, Petkov VI. Breast cancer-specific mortality (BCSM) in patients with node-positive (N+) breast cancer (BC) treated based on the 21-gene assay in clinical practice [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P6-13-03.