Abstract 4975: Stretching the boundary of Oncotype DX testing

Abstract Background: The predictive value of Oncotype DX in early-stage breast cancer had been well established. Strongest data support the use of chemotherapy for Recurrence Score (RS) 30, with 25-30 deriving some benefit. Those with intermediate RS 16-25 are thought to have a small benefit from chemotherapy, especially premenopausal patients. Tumor size 5 cm is viewed as a high-risk feature regardless of RS. Our goal is to investigate how patients with uncertainty regarding their anticipated recurrence risk were managed at our institution. Methods: We conducted a retrospective analysis to explore the management of non-metastatic HER-2 negative hormone sensitive breast cancer patients diagnosed between 01/2018 50), RS 16-25 compared to RS 26-30 and tumor size 5cm. Patients were compared based on whether they received adjuvant chemotherapy or not. The primary endpoint was the rate of local recurrence. Results: The results of our analysis are illustrated in the table. Studying the premenopausal group, 91. 3% had RS 16; yet 35% of them received chemotherapy. Patients with RS 25 represented 3. 2% of the premenopausal group, 12. 5% of which did not receive chemotherapy. The six recurrences in the premenopausal group were all from the RS 16 subgroup. Comparing the RS 26-30 to the RS 16-25 group, patients were on average older with tumors being on average smaller, yet more patients were treated with chemotherapy; and there were no recurrences noted in both subgroups. Finally, in the tumor size 5 cm group, 91. 4% had RS 16, almost all were premenopausal with many patients being lymph node negative, yet more than half received chemotherapy. Conclusions: In our study we demonstrate that in certain subgroups of early-stage breast cancer there is inconsistency in clinical practice when prescribing chemotherapy to patients factoring in their Oncotype DX scores. There is need for larger trials to guide clinicians on using Oncotype DX in those subgroups of patients. Characteristics, Treatment Pattern and Outcomes of Patient Groups of Interest Characteristics Premenopausal (N=506) RS 16-25 (N=28) RS 26-30 (N=36) Tumor Size 5 cm (N=47) Age, Mean (SD) 42. 65 (5. 46) 44. 71 (3. 85) 63. 56 (9. 65) 42. 02 (6. 14) Age, Range 19 - 49 36 - 49 45 - 79 28 - 57 Mean Tumor Size, mm (SD) 29. 66 (52. 21) 29. 57 (33. 88) 16. 88 (11. 19) 83. 61 (37. 52) Lymph Nodes Positive, n (%) 91 (18. 0%) 2 (7. 1%) 0 (0. 0%) 16 (34. 0%) Received Chemotherapy, n (%) 184 (36. 4%) 7 (25. 0%) 13 (36. 1%) 25 (53. 2%) Local Recurrence, n (%) 6 (1. 2%) 0 (0. 0%) 0 (0. 0%) 0 (0. 0%) Mean Follow- Up, months (SD) 19. 28 (8. 20) 19. 39 (7. 07) 21. 21 (11. 04) 19. 26 (8. 93) Citation Format: Zaid Al-Saheli, Vrushali Dabak. Stretching the boundary of Oncotype DX testing abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 4975.