First results from the OPTIMA phase III randomized non-inferiority trial of test-directed chemotherapy in patients with high clinical risk ER-positive HER2-negative early breast cancer.

500 Background: Tumor gene expression tests are widely used to assist adjuvant chemotherapy decisions for women with early breast cancer (EBC). OPTIMA (Optimal Personalised Treatment of early breast cancer using Multi-parameter Analysis) is an international RCT comparing chemotherapy decisions made with the Prosigna (PAM50) gene expression test with standard treatment in mostly node-positive patients. Methods: Women and men aged >40 recommended to receive chemotherapy for ER+ HER2- EBC with 0-9 involved axillary nodes and T size >30mm if node negative were eligible. Randomization was between standard chemotherapy followed by endocrine therapy (CET) or to a Prosigna test directed chemotherapy decision. Patients with Prosigna ROR score > 60 tumors were assigned CET whilst those with low ROR score (≤60) tumors received endocrine therapy (ET) alone. ET for premenopausal women included ovarian function suppression (OFS) in the absence of chemotherapy-induced ovarian insufficiency. ROR scores were not disclosed, and patients receiving CET were blinded to their randomization. OPTIMA was designed to demonstrate non-inferiority (NI) of 5-year invasive breast cancer free survival (IBCFS) in the test-directed arm with a 3% margin in the per protocol (PP) population using a 5% 1-sided alpha. Control arm testing allowed treatment comparison within the low ROR score population at a 3.5% NI margin. Results: From 16 th Jan 2017 to 12 th Dec 2025 4429 patients were randomized, 2215 to the control arm and 2214 to the test-directed arm of whom 2061 (93%) and 2097 (95%) were included in the respective PP group. Patient characteristics in the PP population were well-balanced; 62% were postmenopausal, 37% premenopausal and 0.8% male. 73% had pN1/pN1sn, 8% had pN0/pN1mi and 19% had pN2 tumors. 68% had low ROR score tumors. With a median follow-up of 3.9 years (interquartile range 2.0-5.9), 280 IBCFS events occurred (141 on control arm; 139 on test directed arm) of which 66% were distant recurrences. The 5-year IBCFS rate in the control arm was 91.5% 95% CI 89.7- 92.9% and 90.4% 95% CI 88.6- 92.0% in the test-directed arm, Hazard Ratio (HR) 0.99 90% CI 0.81- 1.20, NI p = 0.013, thereby meeting the pre-defined NI margin. The corresponding 5-year IBCFS rates for the low ROR score population were 94.9% 95% CI 92.9- 96.4% and 93.7% 95% CI 91.8- 95.2% for the two arms respectively, HR 1.06 90% CI 0.78- 1.46 NI p = 0.0051 again demonstrating non-inferiority. There was no significant outcome heterogeneity between subgroups including for menopausal and nodal status. Conclusions: The OPTIMA trial demonstrates that women and men with ER+ HER2- EBC and ROR score ≤60 tumors can safely avoid chemotherapy. It provides evidence for the utility of test-directed chemotherapy in premenopausal women treated with OFS and patients with high levels of nodal involvement. Clinical trial information: ISRCTN42400492.