Abstract C069: Real World Experience of Recurrence Score Oncotype Dx in Adjuvant Treatment of patients with HR+ HER2- Early Breast Cancer: Delays of initiation of adjuvant chemotherapy in patients with high scores

Abstract Background: Adjuvant chemotherapy (ChT) reduces recurrence in early breast cancer (EBS), but many HR-positive patients may not benefit. The Oncotype Dx assay helps guide treatment by assessing recurrence risk. Real-world data from low-resource countries remain limited. Methods: We retrospectively analyzed HR-positive EBC patients who underwent Oncotype Dx testing between 2019 - 2024. Data collected included tumor characteristics, Oncotype Dx score, and adjuvant treatment decisions including ChT, endocrine therapy (ET), and ovarian function suppression (OFS). Results: Between 2019 - 2024, 163 patients with HR+ HER2- EBC underwent Oncotype Dx testing. Median age 54 years (range 30–78). 98.6% were female. 69% of tumor were T1, 30% T2, 1% T3. 83% had node negative. Ductal type 82%. Ki-67>14% was in 61%. Tumor grade: 18% low, 68% intermediate,14% high. ER+/PR+ were 93% and ER+/PR- 7%. Oncotype Dx scores low (<10) 28%, intermediate (11–25) in 53%, high (≥26) in 19%. Mean and median time from surgery to Oncotype Dx report were 41.5 ± 16.3 and 39 days, respectively; Mean of post-operative ChT initiation was 56.3 ± 20.3 days and median 52.5 days (25-118). Conclusion: Among high score patients (n= 31), 63% received AC-T, 17% TC, and 17% CMF protocol. ET included AI (49%) and tamoxifen (44%). Among patients with high Oncotype Dx score and age <50 (n=11), OFS was used in 73%, with tamoxifen and AI prescribed in 2 and 6 patients, respectively; those without OFS received only tamoxifen (n=3). Patients with intermediate Oncotype Dx score (n=87), 15 recieved ChT (AC-T 7, TC 3, CMF 5) and 13 were <50 years of age. 31 received Tamoxifen alone, 6 received OFS with Tamoxifen, and 7 received OFS with AI. All who recieved OFS 42% (13/31) were <50 years. Our study confirms the significant role of Oncotype Dx Recurrence Score in guiding adjuvant therapy, with 97% of high-risk HR+ EBC patients receiving ChT. However, the average delay in initiating ChT was 52.5 days post-surgery, which may impact outcomes. An ambispective follow-up will assess disease-free survival and the potential benefit of starting chemotherapy within 30 days; OFS use was generally aligned with international recommendations. Citation Format: Kassem Salam, Ali Awada, Ali Zreik, Nagi Saghir, Hiba Moukadem. Real World Experience of Recurrence Score Oncotype Dx in Adjuvant Treatment of patients with HR+ HER2- Early Breast Cancer: Delays of initiation of adjuvant chemotherapy in patients with high scores [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2025 Oct 22-26; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2025;24(10 Suppl):Abstract nr C069.