ASCO26: DNA test could spare breast cancer patients chemo

Millions of women with a breast cancer diagnosis could safely avoid debilitating chemotherapy that would not be effective, thanks to a tumour gene expression test.

The OPTIMA trial, led by researchers at University College London and the University of Glasgow, followed more than 4,400 women aged 40 or above with newly diagnosed breast cancer in the UK, Norway, Sweden, Australia, New Zealand, and Thailand who had genomic testing using Veracyte's Prosigna assay, which measures the activity of 50 genes in tumour tissue.

The results presented at ASCO 2026 showed that among these women with HR-positive, HER2-negative breast cancer, those for whom the test indicated they would not benefit from chemo – and so had hormonal therapy alone – had similar outcomes five years later. Some men with breast cancer did take part in the study, but there were too few to draw firm conclusions for this group.

Overall, invasive breast cancer free survival (IBCFS) was 91.5% in the control arm, treated with standard hormonal therapy and chemo, and 90.4% among those who had hormonal therapy alone, meeting the threshold for non-inferiority.

A comparison between the two treatment approaches in patients with a low Prosigna score – indicating they would not benefit from chemo – revealed a similar pattern, with an IBCFS of 94.8% in the control group and 93.6% among those treated with hormone therapy alone.

"OPTIMA addresses a long-standing challenge in breast cancer care: identifying who truly benefits from chemotherapy and who does not. Our findings show that many patients can safely avoid chemotherapy without compromising their outcomes," said lead investigator Prof Rob Stei of UCL, who presented the results at ASCO.

"These results mark an important and significant step toward more personalised treatment," he added. "For patients, this means many may be spared the physical and emotional burden of chemotherapy and its potential long-term side effects. For health systems, it represents a more efficient and evidence-based use of resources."

Based on their trial, the researchers estimate it could help 5,000 NHS breast cancer patients avoid chemotherapy every year.

The next phase of the OPTIMA trial will explore the use of Prosigna in a younger age group, to see if some premenopausal women with this form of breast cancer could also safely avoid chemo, but that data will not be available for several years.