Abstract PS3-08-28: Real-world evidence on the use of a 21-gene recurrence score assay in patients with HR+/HER2− early breast cancer in japan: a nationwide claims database analysis

Abstract Background: The Oncotype DX® test, 21-gene recurrence score assay, is a commercially available genomic assay that calculates a Recurrence Score® (RS) result ranging from 0 to 100 based on the expression of 21-genes. The RS result provides prognostic information independent of clinicopathological factors and predicts the benefit of chemotherapy (CT) to guide adjuvant treatment decisions in patients (pts) with hormone receptor-positive (HR+), HER2-negative (HER2-) early breast cancer (BC). In Japan, the Oncotype DX test has been reimbursed under public health insurance since September 1, 2023, and is expected to help optimize CT decision-making. However, real-world evidence (RWE) on its clinical use remains limited. This study presents the first large-scale, real-world analysis in Japan using a nationwide claims database to describe clinical and demographic characteristics, as well as treatment patterns associated with the use of Oncotype DX testing. Methods: We conducted a retrospective cohort study of pts with BC who underwent Oncotype DX testing between the start of reimbursement (September 2023) and December 2024 using a nationwide claims database provided by Medical Data Vision Co., Ltd. (Tokyo, Japan), which includes data from approximately 230 acute care hospitals. All Oncotype DX-tested pts were included in the analysis of clinical and demographic characteristics. For treatment pattern analysis, the cohort was limited to those with at least 6 months of follow-up after testing. CT and endocrine therapy (ET) were classified as either neoadjuvant or adjuvant. Results: A total of 3,837 pts with BC who underwent ODX testing following reimbursement were identified. The median age was 57.0 [IQR: 49.0-67.0], including 17 male pts (0.4%), and the median BMI was 22.6 [IQR: 20.3-25.7].The majority of pts had T1 (55.1%) or T2 (40.4%) tumors and were node-negative(N0: 87.4%). Distant metastasis was rare (M1: 0.1%). Whereas 49.9%, 38.7% and 7.0% of pts had Stage IA, Stage IIA or Stage IIB disease, Stage III or IV disease was rare (<1%).Most pts (87.8%) were treated at designated cancer care hospitals. Over half received care at large hospitals with ≥500 beds (53.3%), and 45.8% were treated at mid-sized hospitals with 200-499 beds. Among pts with at least 6 months of follow-up after Oncotype DX testing, 23.2% received adjuvant CT. The most common regimen was ACT (anthracycline, cyclophosphamide, and taxane) (48.4%) followed by TC (taxane, cyclophosphamide) (43.4%). ET was administered to 9.1% of pts as neoadjuvant treatment and to 95.1% as adjuvant treatment. Among pts who received adjuvant ET, aromatase inhibitors were most frequently used (58.0%), followed by selective estrogen receptor modulators (SERMs) alone (21.8%), and a combination of luteinizing hormone-releasing hormone agonists and SERMs (15.9%). Additionally, 36.9% pts received radiation therapy. Conclusion: This study presents the first nationwide RWE on the clinical use of the Oncotype DX test in Japan. The findings indicate that the large majority of pts with BC who undergo Oncotype DX testing receive care at cancer-specialized or large medical centers. Cancer staging and treatment patterns suggest that the Oncotype DX test is being appropriately applied in pts with HR+/HER2- early BC, consistent with current guidelines for personalized treatment. Citation Format: M. Hihara, H. Bando, A. Shimomura, N. Sugiyama, N. Yoshii, R. Kawai, A. Shintani, S. Saji. Real-world evidence on the use of a 21-gene recurrence score assay in patients with HR+/HER2− early breast cancer in japan: a nationwide claims database analysis [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 PS3-08-28.