An international clinical trial suggests that a significant proportion of breast cancer patients could safely avoid chemotherapy thanks to a new DNA-based test.

The study, led by University College London (UCL), involved more than 4,000 newly diagnosed patients aged over 40 across the UK, Norway, Sweden, Australia, New Zealand and Thailand.

Researchers used a genomic test known as Prosigna, which analyses the activity of 50 genes linked to breast cancer growth to estimate the risk of cancer returning.

Based on the results, around two-thirds of participants were classified as low-risk and did not receive chemotherapy, instead being treated with hormone therapy alone.The outcomes showed that the five-year survival rate for patients who avoided chemotherapy was 93.7%, compared with 94.9% for those who did receive it, suggesting minimal difference in survival outcomes.This finding indicates that many patients may be exposed to the harsh side effects of chemotherapy unnecessarily.

These side effects can include fatigue, nausea, hair loss, weakened immunity, and fertility complications, all of which significantly affect quality of life.

The researchers also estimate that more than 5,000 NHS patients annually in the UK could potentially avoid chemotherapy if the approach is adopted more widely.

Clinicians involved in the study argue that treatment decisions should increasingly be guided by tumour biology rather than traditional clinical indicators alone.However, it remains unclear whether the findings apply to patients under 40, with further research still required.Experts describe the results as a step towards more personalised and less invasive cancer treatment strategies.