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Breaking research: Gene test can spare many breast cancer patients from chemotherapy

Breast Cancer Trials

Embargoed until Sunday May 31: 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, a large international clinical trial has found.

The OPTIMA trial (Optimal Personalised Treatment of early breast cancer using Multi-parameter Analysis), run by Breast Cancer Trials in Australia, was designed to safely reduce the use of unnecessary chemotherapy for people with newly diagnosed breast cancer. It 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 (ASCO) meeting in Chicago on May 30 (local time), suggest that people aged 40 and over, whose tumours have a low Prosigna test score, can be treated safely with hormone blocking therapy alone, potentially transforming care for thousands of patients each year.

Australian Study Chair, A/Prof Belinda Kiely, explained that the trial has 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,” A/Prof Kiely 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. The results mark a significant step toward more personalised treatment.”

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. 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. Unlike previous studies, which have focused on people with no or limited lymph node involvement, most people in OPTIMA had cancer that had spread to the lymph nodes in their armpit, which placed them at higher risk of future recurrence. Because of this, their usual treatment would include both chemotherapy and hormone blocking treatment taken for five to ten years. Radiotherapy and other treatments were given as usual to all participants.

Participants in OPTIMA were randomly assigned to one of two groups:

• Standard treatment group: patients received chemotherapy followed by hormone blocking therapy.
• Test‑directed group: patients 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.

The trial was designed to compare the number of people whose cancer returned or who died within five years in the test-directed group compared to the standard treatment group. In consultation with patients and clinicians, the researchers defined an acceptable difference as no more than 3%.

Key findings

Of the 4,429 people who took part in the trial, more than two-thirds (68%) had a low Prosigna score.

For this group, the results showed that outcomes 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
• 93.6% of those treated with hormone blocking therapy alone were also alive and recurrence-free

A statistical test showed that at the most, only 2% of patients with a low Prosigna score treated with chemotherapy will benefit from this treatment.

Impact

The results show that people aged 40 or older with hormone‑receptor positive breast cancer and a low Prosigna score can safely avoid chemotherapy.

The research team also found similar outcomes for pre‑ and post‑menopausal women. Premenopausal women all received hormone blocking therapy that included ovarian function suppression, which the researchers believe explains why chemotherapy did not appear to offer additional benefit in this group.

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.

About us:

Founded in 1978, Breast Cancer Trials conducts a multicentre national and international clinical trials research program into the treatment and prevention of breast cancer. Every breast cancer treatment available today has been proven through clinical trials research. The work of Breast Cancer Trials has improved the treatment of breast cancer, led to changes in the way breast cancer is managed and has saved thousands of lives. More than 1,000 researchers in 118 institutions across Australia and New Zealand are committed to the vision of no more lives cut short.

Contact details:

Sara McGregor

Media & PR Lead

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E: [email protected]