A major international study has found that millions of breast cancer patients could safely avoid chemotherapy through the use of a DNA-based gene test that identifies who is most likely to benefit from the treatment.

Researchers found that more than two-thirds of participants could be treated with hormone therapy alone, sparing them the common side effects of chemotherapy, including fatigue, nausea, hair loss, weakened immunity, and fertility issues.

The study, led by University College London, involved more than 4,000 newly diagnosed breast cancer patients over the age of 40 across the UK, Norway, Sweden, Australia, New Zealand, and Thailand.

Scientists used a gene test known as Prosigna to analyse the activity of 50 genes linked to breast cancer growth and assess the risk of the disease returning.

Patients who received a low-risk score did not undergo chemotherapy, and their five-year survival rate was 93.7%, compared with 94.9% among those who received chemotherapy as part of their treatment.

Researchers say the findings could lead to more personalised breast cancer care, with more than 5,000 patients a year in the UK potentially able to avoid chemotherapy while still achieving excellent outcomes.