This ‘Practice-Changing’ Gene Test Could Tell Doctors Which Patients With Breast Cancer Can Skip Chemo, Clinical Trial Suggests

Chemotherapy comes with debilitating side effects, including brain fog, nausea and nerve damage. New research suggests that many people with a common type of breast cancer need just radiation and hormone therapy to prevent recurrence

Margherita Bassi | Daily Correspondent

June 17, 2026 10:01 a.m.

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Chemotherapy can save lives, but it takes a heavy toll on patients with cancer. Common side effects include hair loss, brain fog, nausea, vomiting and nerve damage, and it comes with long-term risks.

Now, a late-stage clinical trial suggests that the majority of women ages 40 and up with the most common type of early breast cancer can forego this aggressive treatment. The results indicate that an existing DNA test called Prosigna—which assesses gene activity associated with cancer—can reveal which patients will benefit just as much from hormone therapy and radiation therapy as they would from those combined with chemotherapy. The findings, presented on May 30 at the American Society of Clinical Oncology annual meeting, could change oncology guidelines and spare many people the brutal impact of chemotherapy.

“This is not a story about getting rid of chemotherapy. It is about using it more wisely,” Justin Stebbing, an oncologist at Anglia Ruskin University in England who did not participate in the research, writes for the Conversation. “The gene test helps protect those high‑risk patients by flagging that they really do need chemotherapy, and at the same time, it protects low‑risk patients from being overtreated.”

The clinical trial, called the OPTIMA trial, involved nearly 4,500 participants in the United Kingdom, Norway, Sweden, Australia, New Zealand and Thailand. The women and handful of men enrolled were at least 40 years old and diagnosed with a type of breast cancer fueled by hormones. They underwent surgery to remove their tumors, but most were considered at high risk of the cancer returning because it had spread to nearby lymph nodes.

To prevent that, standard post-surgery treatment includes chemotherapy, radiation therapy and hormone tablets. In the study, however, participants were divided into a standard treatment group and a test-directed group, where patients received therapies based on their Prosigna test scores. The assessment gauges the activity of 50 genes associated with breast cancer progression, and patients with higher scores have a higher risk of cancer returning.

Almost 70 percent of all participants received low Prosigna scores. Low-scorers who had been assigned to the test-directed group skipped the chemo treatment. When one patient in that group, Karen Bonham, learned she’d be foregoing the brutal therapy, a wave of emotion hit her.

“How to describe the initial feeling? Immense relief? Like Christmas? Certainly a mixture of the two,” she tells the Guardian’s Andrew Gregory. All patients, Bonham included, received hormone therapy and radiotherapy.

OPTIMA: Optimal Personalised Treatment of early breast cancer usIng Multi-parameter Analysis.

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Analyses revealed little difference in outcomes between low-Prosigna-scoring patients who did and did not receive chemotherapy. Five years after treatment, nearly 94 percent of those who skipped chemo were alive and didn’t experience recurrence, similar to the almost 95 percent of low-scorers in the control group who underwent the aggressive treatment. A statistical test suggests that only up to 2 percent of low-scoring patients will draw benefits from chemotherapy, per a statement.

Additionally, results were similar for both pre- and post-menopausal women, and the team didn’t note any differences linked to the number of impacted lymph nodes. There were too few men in the trial to yield solid conclusions among them.

The findings are “practice-changing,” says David Miles, a breast oncologist who advises the U.K.’s National Institute for Health and Clinical Excellence and did not participate in the trial, to the BBC’s Newshour. “We used to give chemotherapy to 100 women to benefit 10, knowing that 90 didn’t need it. … We can now confidently predict many patients will get no benefit at all, and therefore there’s no need for them to have the chemotherapy.” 

Paul Kelly Marcom, medical director for breast cancer at Veracyte, the company that developed the Prosigna test, agrees. “These findings have the potential ​to transform how clinicians treat a large population of patients with breast cancer, helping them to personalize their patients’ treatment choices,” Marcom tells Reuters’ Nancy Lapid.

Margherita Bassi | Read More

Margherita Bassi is a freelance journalist and trilingual storyteller. Her work has appeared in publications including BBC Travel, Discover magazine, Live Science, Atlas Obscura and Hidden Compass.