Associations Between the 21-Gene Oncotype DX Recurrence Score, Ki67, and Race in Early Breast Cancer: An Analysis of the National Cancer Database

Purpose: The study examines the association between the Oncotype DX recurrence score (RS) and Ki67 expression across racial groups using the National Cancer Database (NCDB) to understand racial disparities in hormone receptor (HR)-positive, HER2-negative early breast cancer (EBC). Methods: Women with HR-positive, HER2-negative EBC and 0–3 positive lymph nodes diagnosed in 2018–2019 in the NCDB were included. RS was categorized as low (0–10), intermediate (11–25), and high (26–100); Ki67 as low (≤5%), intermediate (6–29%), and high (≥30%). Wilcoxon and chi-square tests assessed differences; Fleiss’ Kappa measured RS–Ki67 concordance by race. Results: Among 43,898 patients, 17% were node positive. The cohort was 78% Non-Hispanic White (NHW), 8% Non-Hispanic Black (NHB), 6% Hispanic, and 4% Asian American/Pacific Islander (AAPI). RS and Ki67 distributions differed significantly by race, with NHB patients showing the highest proportions of high RS and Ki67 (p<0.0001). Overall agreement was slight (Kappa=0.19, p<0.0001), with fair agreement for high RS and high Ki67 (Kappa=0.35, p<0.0001). Stratified by race, agreement remained slight for NHW, Hispanic, and AAPI patients, but was fair for NHB patients (Kappa=0.24, p=0.002). The strongest concordance between high RS and high Ki67 was seen in NHB patients (Kappa=0.39, p<0.0001). Conclusions: In this NCDB cohort, Ki67 and RS were only slightly concordant overall, with fair agreement observed among patients with high Ki67 and RS. The strongest agreement between Ki67 and RS was noted in the Black subgroup compared to other races, likely due to the higher proportion of patients with high Ki67 and RS in this subgroup.