Abstract Background: Oncotype DX testing plays a central role in guiding adjuvant treatment decisions for patients with early-stage estrogen receptor-positive (ER+), HER2-negative, node-negative (N0) breast cancer. While the assay informs chemotherapy decisions and may help avoid overtreatment, delays in ordering or resulting may contribute to postponed therapy initiation. This study characterizes the timing of Oncotype DX testing in relation to surgery and evaluates its association with initiation of chemotherapy, endocrine therapy (ET), and radiation therapy (RT). Methods: We conducted a retrospective review of 373 ER+/HER2–/N0 breast cancer patients treated at a single academic center between January 2018 and November 2024. Inclusion required an Oncotype DX order and available treatment dates. Patients treated externally or with missing key dates were excluded. Data collected included demographics, tumor characteristics, and dates of definitive surgery, Oncotype DX order/result, and treatment initiation. The primary outcome was time from surgery to first treatment. We also evaluated intervals from surgery to Oncotype order/result and from result to treatment. Results: The cohort had a mean age of 58.9 years (range 30–88) and was predominantly female (98.9%). Racial/ethnic distribution was 57.7% White, 31.3% Black, and 43.3% Hispanic. Most tumors were stage IA (90.1%) with low (55.6%) or intermediate (31.8%) recurrence scores. Oncotype DX was ordered before surgery in 40 patients (8.6%), on the day of surgery in 105 (22.5%), and a mean of 30.2 days postoperatively (SE 2.59) in the remainder. Results became available a mean of 41.1 days after surgery (SE 1.33), excluding 21 patients with preoperative results and one with same-day result. Chemotherapy was the first treatment in 65 patients, initiated a mean of 64.2 days after surgery and 33.7 days after the Oncotype result. ET was first in 135 patients; 13 began therapy preoperatively and 29 started before Oncotype results. Among those who initiated ET postoperatively and post-result, the mean time to treatment was 61.3 days after surgery and 36.4 days after result. RT was the first treatment in 173 patients, excluding 70 who received intraoperative RT. Among these, RT began a mean of 63.8 days after surgery and 28.8 days after Oncotype result. Two patients began ET and RT on the same day, averaging 41 days post-surgery and 25.5 days post-result. Conclusion: Delays in Oncotype DX ordering and resulting were associated with prolonged time to treatment. Patients with earlier testing had shorter delays. When compared to national guidelines, many patients initiated therapy later than recommended. Adjuvant chemotherapy is ideally started within 4–6 weeks and no later than 12 weeks post-surgery; our cohort averaged over 9 weeks, with some beyond 12 weeks. RT is recommended within 6–8 weeks of surgery (or 4–6 weeks post-chemotherapy), but was frequently delayed. While ET is more flexible, most patients started beyond 6 weeks. Workflow adaptations during the COVID-19 pandemic, including use of core-biopsy Oncotype testing and neoadjuvant ET to bridge surgical delays, may have contributed to these patterns. Early integration of Oncotype testing into the surgical workflow may reduce treatment delays and improve adherence to care timelines. Citation Format: E. Kohilakis, J. Taylor, S. Jao, E. Hakim, M. Rony, L. Coe, S. Harbour, N. Degrezia, A. Brooks, S. Feldman, A. Gupta, E. Ravetch, M. Sheckley, M. McEvoy. Timing of Oncotype DX Testing and Its Impact on Treatment Initiation in ER+/HER2-/N0 Breast Cancer Patients 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 PS5-11-23.
Kohilakis et al. (Tue,) studied this question.