Millions of breast cancer patients could safely avoid chemotherapy as scientists have developed a DNA test that can distinguish between patients who are likely to benefit from the treatment and those who are not, according to results from a landmark international trial presented at the American Society of Clinical Oncology’s annual meeting on Saturday. The study, led by University College London, involved more than 4,000 newly diagnosed patients over the age of 40 across six countries. Researchers used a gene test called Prosigna to measure the activity of 50 genes involved in breast cancer growth. More than two-thirds of participants received low scores and were treated with hormone therapy alone, achieving a five-year survival rate of 93.7% — statistically indistinguishable from the 94.9% rate among those who received chemotherapy.

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What the Trial Found

The Prosigna test calculates a patient’s risk of breast cancer recurrence by measuring the activity of 50 genes. The trial enrolled patients with early-stage breast cancer that had spread to nearby lymph nodes — the population for whom chemotherapy has long been the standard recommendation.

Those who received a low score, two-thirds of the group, were not treated with chemotherapy. Their survival rate differed from the chemotherapy group by just 1.2 percentage points, a gap that was not statistically significant UCL clinical trial results, 30 May 2026.

Professor David Miles, a leading cancer specialist, described the findings as “practice-changing.” He told the BBC: “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. We used to give chemotherapy to 100 women to benefit 10, knowing that 90 didn’t need it.”

UCL estimates that more than 5,000 NHS patients a year could avoid chemotherapy as a result of the trial. The findings do not yet apply to patients under 40, with data for younger women still several years away.

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The Patient Experience

Karen Bonham, 64, from Cardiff, took part in the trial and avoided chemotherapy after receiving a low Prosigna score. She received radiotherapy and hormone therapy for over eight years. “Cancer diagnosis and treatment can be shocking,” she said. “It certainly propels you into a world of uncertainty. Life priorities realign you, simply want to survive.”

Tanya Hutson, who was diagnosed with breast cancer in 2022 and had chemotherapy as part of her treatment, called the new DNA test “absolutely amazing.” She said, “It just proves what happens when money is put into research. For all these people out there who don’t need it but are still getting it — it’s an absolute game changer.” She described chemotherapy as having been “brutal” BBC patient interviews, May 2026.

Chemotherapy can cause fatigue, nausea, hair loss, a weakened immune system, and fertility issues. The primary treatment for breast cancer is usually surgery to remove tumours, with chemotherapy often recommended afterwards to reduce the risk of recurrence.

The hidden cost of overtreatment when the standard of care causes more harm than benefit

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The Implementation Challenge

The trial’s results arrive with the evidence clear, but the guidelines are yet to be written. Clinical guidelines take time to change. Oncologists who have spent decades recommending chemotherapy for node-positive breast cancer will need to be convinced that a genomic test can reliably identify patients who derive no benefit.

The Prosigna test is already available. The question is how quickly it becomes the standard of care.

The NHS has a structural advantage: centralised guideline-setting and a single-payer system that could mandate testing as a condition of chemotherapy approval. The US system, fragmented across insurers and providers, will adopt unevenly. The equity gap will be geographic and economic. Women who avoid chemotherapy will be those whose oncologists order the test. Women who receive unnecessary chemotherapy will be those whose oncologists do not.

The global figure, if the test were adopted universally, would be in the millions. Each avoided course of chemotherapy saves the patient months of toxicity. It saves the health system the cost of administering the drugs, managing the side effects, and treating complications.

The trial was not testing a new drug. It was testing the withdrawal of an old one. The result was not that a treatment worked. It was thought that a treatment was unnecessary.

The evidence-to-practice gap — why clinical guidelines lag behind clinical trials

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FAQ: Breast Cancer Chemotherapy Study 2026

What is the Prosigna test?

The Prosigna test is a genomic test that measures the activity of 50 genes involved in breast cancer growth. It calculates a patient’s risk of the disease returning and identifies those who are unlikely to benefit from chemotherapy.

How many patients could avoid chemotherapy?

UCL estimates more than 5,000 NHS patients per year. Globally, if the test were adopted universally, the number would be in the millions. Two-thirds of trial participants received low scores and were safely treated without chemotherapy.

What were the survival rates?

The five-year survival rate for patients who avoided chemotherapy was 93.7%, compared with 94.9% for those who received it, a statistically insignificant difference.

Does this apply to all breast cancer patients?

The trial involved patients over 40 with early-stage breast cancer that had spread to nearby lymph nodes. Data for patients under 40 is not yet available and is several years away.

When will the test be available?

The Prosigna test is already available. The question is how quickly clinical guidelines will incorporate it as a standard prerequisite for chemotherapy decisions.

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Written by the Health Desk, drawing on UCL clinical trial data, interviews with Professor David Miles, patient testimony from Karen Bonham and Tanya Hutson, and presentations at the American Society of Clinical Oncology annual meeting. The desk has covered oncology and genomic medicine for over a decade.