ASCO 2026: OPTIMA Phase 3 — Genomic Testing Allows 68% of Breast Cancer Patients to Safely Skip Chemotherapy Without Worse Outcomes

The OPTIMA Phase 3 trial, presented at ASCO 2026, enrolled 4,429 patients with early-stage ER-positive/HER2-negative breast cancer — the most common breast cancer subtype — who were traditionally recommended to receive chemotherapy based on clinical risk factors. Using the Prosigna gene expression test to classify patients into low or high genomic risk, the trial showed that 68% of the enrolled patients had low genomic risk and could safely receive hormone therapy alone without adjuvant chemotherapy. The primary endpoint of non-inferiority was met: 5-year invasive breast cancer-free survival was 93.6% with hormone therapy alone versus 94.8% with chemotherapy plus hormone therapy — within the pre-specified non-inferiority margin. Overall population 5-year IBCFS was 91.5% vs. 90.4%. The trial was conducted primarily through the NHS Cancer Research UK framework and could spare over 5,000 NHS patients annually from chemotherapy. The result validates genomic testing as the standard basis for chemotherapy decisions in early breast cancer in clinically high-risk but genomically low-risk patients, confirming a practice shift already underway based on earlier Oncotype DX evidence (TAILORx, RxPONDER) and extending it to a broader genomically-defined population with Prosigna. Chemotherapy carries substantial risks including fatigue, neuropathy, bone marrow suppression, and rare treatment-related leukemia — avoiding it in two-thirds of early breast cancer patients is clinically and quality-of-life meaningful.