A new genomic test could spare millions of women chemotherapy for breast cancer, after the largest trial of its kind demonstrated that many patients with the most common form of the disease can safely skip the toxic treatment without raising their risk of recurrence.
Breast cancer is the world’s most prevalent cancer, with around 59,400 new cases diagnosed each year in the UK alone, affecting roughly one in seven women. Standard treatment involves surgery to remove tumours, followed by chemotherapy when doctors judge there is a significant risk the disease will return. But chemotherapy comes with a gruelling catalogue of side-effects – hair loss, rashes, nausea, insomnia, fatigue, and potentially life-changing consequences such as infertility, cognitive impairment, early menopause, heart problems and even leukaemia. For decades, patients had little choice but to endure them.
Now scientists have developed a test that reads the genetic activity of a tumour and gives doctors a clear, personalised answer: whether chemotherapy will offer any real benefit or can be safely avoided. The breakthrough paves the way for a new era of precision medicine in breast cancer care, sparing hundreds of thousands of women worldwide each year from unnecessary toxicity.
How the Prosigna test identifies patients who can skip chemotherapy
The test, called Prosigna and manufactured by the global diagnostics company Veracyte, analyses the activity of 50 genes in a sample of tumour tissue. It determines the tumour’s molecular subtype – classifying it as Luminal A, Luminal B, HER2-enriched or Basal-like – and produces a Risk of Recurrence (ROR) score. This score estimates the probability that the cancer will return within the next decade, allowing doctors to weigh precisely whether the marginal benefit of chemotherapy justifies its harms.
The test is designed specifically for patients with early-stage, hormone-receptor positive (HR+), HER2-negative breast cancer – the most common form, accounting for up to 80% of all breast cancer cases globally. In the UK, about 70% of breast cancers are oestrogen-receptor positive, the sub-group for which the test is most relevant. By using tumour biology rather than traditional clinical features alone to guide decisions, the test offers a level of personalisation that has not previously been possible at scale.
International trial delivers practice-changing evidence
Evidence for the test’s effectiveness comes from the Optima trial, an international, randomised, partially-blinded Phase 3 study led by University College London. The trial enrolled 4,429 patients aged 40 or over across the UK, Norway, Sweden, Australia, New Zealand and Thailand. All participants had newly diagnosed hormone-positive breast cancer. Some men also took part, but their numbers were too small to draw firm conclusions.
Patients were randomly assigned to one of two treatment groups. In the standard group, everyone received chemotherapy followed by hormone therapy. In the second group, each patient’s tumour was analysed using the Prosigna test. Those with a high ROR score received chemotherapy and hormone therapy; those with a low score were treated with hormone therapy alone. Radiotherapy and other treatments were given as usual in both groups.
Five years after treatment, the results were remarkably similar. Among patients in the standard group who received chemotherapy, 95% were alive and free from breast cancer recurrence. In the test-guided group, 94% of those who skipped chemotherapy based on their low score were also alive and recurrence-free – a difference so small that it confirms non-inferiority. For patients with low ROR scores, the invasive breast cancer-free survival rate was 94.9% with hormone therapy alone compared with 93.7% when chemotherapy was added, meaning chemotherapy offered little or no additional benefit.
One woman who took part in the trial described the relief of being told she could avoid chemotherapy as feeling “like Christmas”. Nine years after her diagnosis, having taken the test and skipped the treatment, she remains healthy and fully active.
The findings were presented at the American Society of Clinical Oncology’s annual meeting in Chicago, the world’s largest cancer conference, and have been hailed as practice‑changing. Further data on overall survival and comorbidity outcomes are expected to be presented at the same conference in 2026.
Professor Rob Stein, the trial’s chief investigator and a professor of breast oncology at UCL, said: “Optima addresses a longstanding challenge in breast cancer care: identifying who truly benefits from chemotherapy and who does not. Our findings show that many patients can safely avoid chemotherapy without compromising their outcomes.
“These results mark an important and significant step toward more personalised treatment. The trial has successfully used tumour biology to guide decisions rather than relying solely on traditional clinical features. For patients, this means many may be spared the physical and emotional burden of chemotherapy and its potential long-term side-effects. For health systems, it represents a more efficient and evidence-based use of resources.”
Professor Iain MacPherson, co-chief investigator and professor of breast oncology at the University of Glasgow, added: “Optima provides robust, practice‑changing evidence that we can safely reduce the use of chemotherapy for many patients with hormone‑sensitive breast cancer. These findings represent a major step forward in delivering more personalised, precise care, ensuring that treatment decisions are driven by what will genuinely improve outcomes for patients, while avoiding unnecessary toxicity. The potential impact for both patients and health services is substantial.”
The trial received funding from the National Institute for Health and Care Research (NIHR), Veracyte, and cancer charities. The Prosigna test is already available in some countries and is expected to become available in the United States from June 2026. In the UK, the NHS is also rolling out complementary innovations such as liquid biopsy blood tests to speed up access to targeted therapies, and the Personalised Breast Cancer Programme at Addenbrooke’s Hospital in Cambridge is using whole genome sequencing of tumour DNA to tailor treatment further. These developments, combined with the Optima results, signal a fundamental shift away from one-size-fits-all chemotherapy toward treatment that is precisely matched to the biology of each woman’s cancer.