Scientists in Oxford have discovered a new method for identifying people most at risk of breast cancer.
Breast cancer patients have higher numbers of regulatory T cells
Doctors at the John Radcliffe Hospital claim breast cancer sufferers have a higher number of certain immune cells in their breast tissue.
These cells stop the body's immune system from fighting the disease.
The research says such high-risk patients are unlikely to respond well to current treatments, including hormone therapy such as tamoxifen.
The work, funded by the Breast Cancer Campaign, was conducted by Gaynor Bates and Alison Banham.
It focuses on the immune cells called regulatory T cells, which normally work to stop the immune system attacking the body's own tissue.
But, in breast cancer patients the regulatory T cells are found in higher numbers and prevent the immune system from recognising and attacking cancerous cells.
Dr Bates said: "In the future I hope this research could help clinicians identifying those patients who will not respond well to current treatments and are at risk of later relapse so they can receive more frequent monitoring and appropriate treatments."
Pamela Goldberg, chief executive of Breast Cancer Campaign, said the charity was delighted to support such "groundbreaking work".
She added: "It is vitally important that new and accurate ways of identifying those whose breast cancer is likely to return are developed."