A trial has found many people with breast cancer can safely avoid chemotherapy with the use of a gene test, potentially sparing them unnecessary side effects without increasing the risk of the cancer returning.
The OPTIMA (Optimal Personalised Treatment of early breast cancer using Multi-parameter Analysis) trial, followed more than 4,400 patients worldwide, including 263 patients from Australia and New Zealand.
The findings, presented at the 2026 American Society of Clinical Oncology on May 30 suggest that people aged 40 and over, whose tumours have a low Prosigna test score, can be treated safely with hormone blocking therapy alone.
Australian study Chair, Associate Professor Belinda Kiely, explained that the trial had successfully used tumour biology to guide treatment decisions rather than relying solely on traditional clinical features.
“OPTIMA addresses a long-standing challenge in breast cancer care: identifying who benefits from chemotherapy and who does not,” she said.
“These findings show that chemotherapy offers little or no additional benefit for people with low Prosigna scores, meaning a substantial number of patients could safely avoid it and its physical and emotional side effects without compromising their outcomes.”
Assoc Prof Kiely said the results marked a significant step toward more personalised treatment for breast cancer.
Chemotherapy is regularly offered to people with early‑stage breast cancer that has spread from the breast to nearby lymph nodes, as it lowers the risk of the disease returning.
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While effective overall, there is concern that many people with hormone‑receptor positive breast cancer, the most common type of breast cancer, receive little or no benefit from chemotherapy but still experience its significant side effects.
OPTIMA set out to address this dilemma by using a genomic test from Veracyte called Prosigna, which measures the activity of genes involved in breast cancer growth.
The test is performed on cancer tissue samples.
Typically, these are tumours removed at surgery but as the test uses very little tissue, it also works on diagnostic needle biopsies.
The OPTIMA trial recruited women and men aged 40 or older following surgery for hormone-receptor positive breast cancer.
In addition to the standard treatment group of patients who received chemotherapy followed by hormone blocking therapy, a test‑directed group had their tumour tested using Prosigna.
Those with a high score (above 60) received chemotherapy and hormone blocking therapy, while those with a low score (less than or equal to 60) were treated with hormone blocking therapy alone.
Radiotherapy and other treatments were given as usual to all participants.
More than two-thirds (68%) of patients who took part in the trial had a low Prosigna score.
The results showed that outcomes for this group were very similar whether chemotherapy was given or not.
Five years after treatment 94.8% of those who received chemotherapy alongside hormone blocking therapy were alive and free from breast cancer recurrence, while 93.6% of those treated with hormone blocking therapy alone were also alive and recurrence-free
A statistical test showed that at most, 2% of patients with a low Prosigna score treated with chemotherapy would benefit from this treatment.
It is not yet known whether the findings apply to people under the age of 40.
The next phase of OPTIMA aims to provide further information about test use for premenopausal women.
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