Gene-screening has been used to identify women most likely to benefit from one type of breast cancer chemotherapy.
The technique could lead to a simple test enabling doctors to administer personalised treatment, say researchers.
In future the same method may offer a way of predicting which patients will respond to other cancer drugs.
This in turn could make expensive new treatments more cost-effective and available on the NHS, say researchers.
The international team of scientists scanned 829 genes in breast cancer tumour cells.
They selected six which, if missing or faulty, would prevent the chemotherapy agent paclitaxel working properly.
A patient study then showed how the genes could reveal in advance which women were likely to respond best to the drug.
Lead researcher Dr Charles Swanton, from the Cancer Research UK charity’s London Research Institute, said: “Our research shows it is now possible to rapidly pinpoint genes which prevent cancer cells from being destroyed by anti-cancer drugs and use these same genes to predict which patients will benefit from specific types of treatment.”
Each year more than 45,500 women are diagnosed with breast cancer in the UK, and around 12,000 die from the disease. About 15% of these patients will be prescribed paclitaxel.
The new findings, reported in The Lancet Oncology medical journal today, suggest that half the women currently prescribed the drug could do without it.