A massive international study suggests that many people with the most common type of breast cancer may not need chemotherapy after surgery and can do just as well on hormone therapy alone. A genomic test developed by South San Francisco company Veracyte appears to reliably flag tumors that are unlikely to benefit from chemo, potentially sparing millions of patients from the treatment’s intense short- and long-term side effects.
The randomized OPTIMA trial, led by University College London, enrolled more than 4,400 patients across the UK, Norway, Sweden, Australia, New Zealand and Thailand, according to UCL. The results were presented at the 2026 American Society of Clinical Oncology meeting and, as reported by ASCO Post, investigators said the test-guided strategy met the trial’s noninferiority goals for cancer-free survival.
OPTIMA used Veracyte’s Prosigna (PAM50) assay to generate a Risk of Recurrence (ROR) score and sorted about two-thirds of participants into a low-risk group. Those low-risk patients who received endocrine (hormone) therapy alone had roughly 93.7% five-year invasive breast-cancer-free survival, compared with about 94.9% for patients who had both chemotherapy and hormone therapy, which met the trial’s prespecified noninferiority margins, according to a sponsor release from Veracyte. Investigators reported a median follow-up of just under four years and said the findings held up across multiple subgroups, including some premenopausal patients who were also receiving ovarian suppression.
What the Prosigna Test Looks For
The Prosigna assay analyzes the activity of 50 genes to assign an ROR score that reflects the underlying tumor biology, rather than relying on clinical features alone. In OPTIMA, the research team used an ROR cutoff of 60 to decide who could safely forgo chemotherapy. Patients described feeling enormous relief when told they could skip chemo and stay on hormone therapy only, according to The Guardian.
What This Means for Patients and Doctors
Oncologists have called OPTIMA practice-changing, but they also caution that real-world adoption of the Prosigna-guided strategy will hinge on updated clinical guidelines, insurance coverage and longer follow-up, and they have flagged concerns such as the relatively short median follow-up and a trial population that was mostly White, per OncLive. Veracyte notes that Prosigna is already available through its CLIA-certified labs in California, but many patients in the United States still face open questions about access and cost.
Los Angeles surgical oncologist Dr. Farin F. Amersi discussed the results and what they might mean in everyday clinics on CBS Los Angeles. Experts stress that patients should not change a recommended treatment plan on their own and advise asking your oncology team whether genomic testing like Prosigna is appropriate for your specific tumor type and stage.
