Practice-changing evidence could spare many breast cancer patients chemotherapy

Many people with breast cancer can safely avoid chemotherapy through the use of a genomic test, without increasing the risk of disease recurrence.

The findings relate to women diagnosed with early-stage hormone receptor-positive (ER-positive) HER2-negative breast cancer, the most common subtype of the disease. These patients are typically offered a combination of chemotherapy and endocrine therapy to reduce the risk of cancer recurrence. While this combined approach is broadly effective, clinicians have long recognised that this patient cohort derive little or no benefit from chemotherapy, despite still being exposed to its substantial toxicities.

The OPTIMA trial (Optimal Personalised Treatment of early breast cancer using Multi-parameter Analysis), led by Breast Cancer Trials in Australia, followed more than 4,400 patients internationally, including participants from Australia and New Zealand. Presented at the 2026 American Society of Clinical Oncology (ASCO) meeting in Chicago, the results suggest that patients aged 40 and over whose tumours have a low Prosigna test score could be treated safely with hormone-blocking therapy alone.

A/Professor Belinda Kiely, medical oncologist and Australian study chair, said the trial demonstrates the growing role of tumour biology in guiding treatment decisions, rather than relying only on traditional clinical indicators.

“OPTIMA addresses a long-standing challenge in breast cancer care: identifying who benefits from chemotherapy and who does not,” stated A/Professor Kiely. “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.”

The Prosigna genomic test, developed by Veracyte, is performed on tumour tissue samples, typically taken during surgery, although it can also be used on diagnostic needle biopsies due to the small amount of tissue required. Unlike earlier studies that focused primarily on patients with no or limited lymph node involvement, most participants in OPTIMA had cancer that had spread to lymph nodes in the armpit, placing them at higher risk of recurrence.

Among the participants, more than two-thirds (68%) were classified as having a low Prosigna score. In this group, outcomes were similar regardless of whether chemotherapy was administered.

At five years post-treatment, 94.8% of patients who received chemotherapy alongside hormone-blocking therapy were alive and free from breast cancer recurrence, compared with 93.6% of those treated with hormone-blocking therapy alone. A statistical analysis indicated that, at most, only 2% of patients with a low Prosigna score receiving chemotherapy would derive benefit from the treatment.

The trial also reported comparable outcomes between pre- and post-menopausal women. All premenopausal participants received hormone-blocking therapy that included ovarian function suppression, a factor researchers believe may explain why chemotherapy did not demonstrate additional benefit in this subgroup.

“OPTIMA sets a new standard for how chemotherapy decisions are made in breast cancer,” said Dr Phillip Febbo, Chief Scientific and Medical Officer at Veracyte. “Prosigna now has the strongest prospective evidence of any genomic test to predict which patients with clinically high-risk hormone-receptor positive breast cancer can safely avoid chemotherapy. For patients, that means the option to choose a treatment with fewer unnecessary side effects, and for clinicians, the confidence to act on it.”

The Medical Services Advisory Committee (MSAC) has previously rejected public funding of Prosigna for predicting breast cancer recurrence for postmenopausal, estrogen receptor (ER) and/or progesterone receptor (PR) -positive, HER2-negative females with breast cancer. The new data is critical for a resubmission.

Karen Bonham, 64, was diagnosed with breast cancer following routine screening in June 2017. Married with two children, she had worked as a speech therapist for 40 years. She became aware of the OPTIMA trial during an early oncology appointment in September 2017, while discussing chemotherapy, a treatment she was dreading.

While walking on a local beach, Karen received a phone call from her hospital telling her she had been allocated to the test-directed group of the trial and did not require chemotherapy.

Instead of chemotherapy, Karen went on to receive radiotherapy and hormone therapy, completing eight years of active treatment. She said, “How to describe the initial feeling? Immense relief? Like Christmas? Certainly a mixture of the two.”

Now almost nine years on from her diagnosis, she said she does not feel defined by cancer and has returned to normal family life. She remains active, enjoying walking and yoga.

The investigators noted that it remains unclear whether these findings apply to patients under the age of 40. Further research is planned, with the next phase of OPTIMA expected to provide additional insight into the role of genomic testing, particularly in younger and premenopausal populations.

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