Real-world Impact of the 21-Gene Recurrence Score on Adjuvant Treatment Decisions in Early Breast Cancer

Background/Aim: The 21-gene recurrence score (RS) assay guides adjuvant chemotherapy decisions in hormone receptor-positive/human epidermal growth factor receptor 2-negative early breast cancer. We evaluated how RS results altered treatment recommendations and were integrated with clinicopathological factors in routine practice. Patients and Methods: We retrospectively analyzed 41 consecutive patients who underwent RS testing for postoperative treatment planning at a single institution. Pre-test and post-test treatment recommendations were compared. Exploratory analyses examined patients with RS ≤25 who received chemotherapy and treatment patterns in node-positive disease. Results: Median age was 58 years; 20 patients (48.8%) had node-positive disease. RS was 0-10 in nine patients (22.0%), 11-25 in 25 (61.0%), and ≥26 in 7 (17.1%). Treatment recommendations changed in 16 patients (39.0%): chemotherapy was omitted in 13 (31.7%) and added in 3 (7.3%). Among 34 patients with RS ≤25, 29 (85.3%) received endocrine therapy alone and 5 (14.7%) received chemo-endocrine therapy. Patients receiving chemotherapy were younger (median 48 vs. 59 years, p=0.049) and had higher RS values (median 17 vs. 13, p=0.007). Among 20 node-positive patients, 15 (75.0%) received endocrine therapy alone. Conclusion: RS testing altered adjuvant treatment recommendations in 39.0% of patients, predominantly through chemotherapy omission. In patients with RS ≤25, younger age and higher RS were associated with chemotherapy use, suggesting that genomic and clinicopathological information were integrated in routine decision-making.