Abstract PS4-09-24: Clinical and economic impact of the 21-gene assay for guiding treatment in patients with HR+/HER2- early breast cancer across racial and ethnic subgroups in the US

Abstract Background: Racial and ethnic disparities in treatment and outcomes persist among breast cancer patients in the United States (US), raising concerns about equitable access to precision oncology tools. The 21-gene assay, which estimates distant recurrence risk and predicts the clinical benefit of chemotherapy for hormone receptor-positive (HR+) and human epidermal growth factor receptor 2-negative (HER2-) early-stage breast cancer, has become a key decision-making tool. This study assessed the clinical and economic value of the 21-gene assay compared to relying on clinical-pathologic risk factors alone, stratified by race and ethnicity. Methods: A validated cost-effectiveness model was adapted to reflect patients with node-negative (N0) or node-positive (N1) HR+/HER2− early breast cancer across four US racial and ethnic subgroups: non-Hispanic Black (NHB), non-Hispanic White (NHW), Asian, and Hispanic. Clinical inputs were derived from published data, including TAILORx, RxPONDER, and the SEER database. Subgroup-specific assumptions were reviewed and confirmed by US clinical experts. Outcomes were expressed as cost per quality-adjusted life year (QALY) over a lifetime horizon. Sensitivity analyses tested the robustness of results. Results: The 21-gene assay was cost-effective across all racial and ethnic subgroups, offering improved outcomes at lower costs compared to clinical-pathologic factors alone. The assay was dominant (lower cost, greater QALYs) in both N0 and N1 populations (Table 1). The greatest cost savings were seen in the N0 NHB subgroup, driven by more precise chemotherapy use and reduced risk of disease progression. Sensitivity analyses supported the robustness of these findings across a range of assumptions and willingness-to-pay thresholds. Conclusions: The 21-gene assay improves patient outcomes and reduces costs compared to using clinical-pathologic assessment alone across diverse racial and ethnic subgroups with HR+/HER2- N0 and N1 early-stage breast cancer. In addition to the clinical benefit observed across all subgroups, the greatest cost savings were observed in the N0 NHB subgroup, highlighting the assay’s potential to support more equitable care and reduce disparities in treatment decision-making. Citation Format: G. Cuyun Carter, C. Moyon, V. Berdunov, M. Gouldson, J. Racz, J. Bennett, O. Kantor, Y. Abdou. Clinical and economic impact of the 21-gene assay for guiding treatment in patients with HR+/HER2- early breast cancer across racial and ethnic subgroups in the US. abstract. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr PS4-09-24.