Do Racial and Income Disparities Exist in the Application of 21-Gene Recurrence Score?

Background: The 21-gene recurrence score is a useful tool to predict the recurrence risk in patients with early hormone receptor positive (HR +) and human epidermal receptor-2 negative (HER2-) breast cancer, which helps to determine those patients who may benefit from chemotherapy. Our goal was to assess whether there was a disparity in the use of the 21-gene recurrence score, especially between races and income levels. Methods: Using the SEER Medicare database, we analyzed breast cancer patients diagnosed from 2012 to 2017. Inclusion criteria were HR + /HER2- phenotype, clinical stages I and II in post-menopausal women, and Stage 1 cancers in premenopausal women. Differences in the application of the 21-gene recurrence score with regard to race and income level were studied using chi-square analysis. Results: Overall, 124 761 patients were included. Of these, 99.1% were females, and 32.9% had 21-gene recurrence score testing. The median age was 70 years (range 27–100). Most patients had invasive ductal carcinoma (86.6%) followed by invasive lobular carcinoma (13.4%), of which 66.0% were stage I and 34.0% as stage II. When comparing subgroups based on testing, White race had a lower application rate (83.8% vs. 84.3%, p = 0.031), compared to African-Americans (8.7% vs. 8.3%, p = 0.031). Similarly, patients with ≥ 10% poverty index showed a lower frequency of testing (46.0% vs. 47.3%, p < 0.001). However, clinically meaningful disparities by race or income were not observed. Underuse of 21-gene recurrence score was more evident among older patients (≥ 65, 76.9% vs. 61%, p < 0.001), separated/divorced/widowed individuals (38.7% vs. 28.4%, p < 0.001), and those undergoing mastectomy (39% vs. 29.5%, p < 0.001) compared to breast-conserving surgery. Conclusions: No clinically significant disparities were observed in race or income level in the application of the 21-gene recurrence score, which is reassuring, particularly as chemotherapy treatment regimens continue to trend appropriately trend toward de-escalation. However, underuse was more evident among older patients, separated/divorced/widowed individuals, and those undergoing mastectomy, highlighting opportunities to improve equity and adherence to guideline-based testing.