Almost half of women with the most common form of early breast cancer could be spared chemotherapy thanks to a genetic test, research suggests.
The Oncotype DX test involves the examination of genes taken from a sample of a tumour removed during surgery.
It can help doctors decide whether chemotherapy would actually benefit patients and the risk of cancer returning.
Research carried out by Simon Holt, a breast surgeon at the Hywel Dda Health Board in Wales, found that 46% of patients with early stage disease could be spared unnecessary chemotherapy.
The 142 NHS patients in his study had oestrogen receptor positive breast cancer, the most common type, and had initially been offered chemotherapy and hormone therapy.
The Oncotype DX test is currently being reviewed by the National Institute for Health and Clinical Excellence (Nice) for widespread use on the NHS.
Mr Holt said: "With nearly 50,000 women diagnosed with early stage breast cancer each year in the UK, a genomic test like Oncotype DX that is capable of predicting treatment benefits and/or outcomes may have an important role to play in improving treatment decision making and ultimately impacting on quality of care.
"Oncotype DX allows us to use our health funds more effectively while sparing patients from unnecessary chemotherapy."
Mr Holt presented his findings at the San Antonio Breast Cancer Symposium last week.