Real-world Utilization of the 21-Gene Assay in Taiwanese Female Patients with Early-Stage Breast Cancer: Experience from a Single Institute

Background: Clinical trials have demonstrated that the 21-gene assay (Oncotype DX) can predict the benefits of adjuvant chemotherapy in patients with hormone receptor-positive (HR+) and human epidermal growth factor 2-negative (HER2−) breast cancer. This study investigated the real-world utilization of this genomic test in Taiwanese patients. Materials and Methods: We compiled data on the recurrence score (RS) and clinicopathological characteristics of patients who received the 21-gene assay between August 2016 and August 2021. Survival outcomes were analyzed using the Kaplan–Meier method and log-rank test. Correlations between clinicopathological characteristics and RSs were analyzed using the Chi-square test or Fisher's exact test. Results: Of the 106 recruited patients, 34 and 72 were classified into different risk groups using conventional and Trial Assigning Individualized Options for Treatment (TAILORx)-based cutoff points, respectively. In the conventional stratification group, 61.8%, 29.4%, and 8.8% of the patients were classified into the low-risk (RS: 0–17), intermediate-risk (RS: 18–30), and high-risk (RS: 31–100) categories, respectively. In the TAILORx stratification group, 18.1%, 72.2%, and 9.7% of the patients were classified into the low-risk (RS: 0–10), intermediate-risk (RS: 11–25), and high-risk (RS: 26–100) categories, respectively. In survival analysis, recurrence-free survival did not significantly differ among discrete risk categories. The high-risk category determined using TAILORx-based cutoff points was associated with the presence of >14% Ki-67-positive cells (P = 0.004) and tumor histology Grade III (P = 0.001). Conclusion: Using the Oncotype DX assay, we classified a small proportion of our Taiwanese patients into the high-risk category; no survival difference was observed among the patients in distinct risk categories. These results suggest the clinical utility of the 21-gene assay in Taiwanese patients with early HR+/HER2−breast cancer.