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, according to the international team of scientists.
Researchers 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: “Since the whole human genome was sequenced, scientists have been trying to understand the role of each of the 21,000 genes contained within it.
“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, suggest that half the women currently prescribed the drug could do without it.
Dr Swanton added: “Now the challenge is to apply these methods to other drugs in cancer medicine and to help identify new drugs within clinical trials that might benefit patients who are predicted to be unresponsive to treatment.
“These could include treatments that are currently deemed too expensive to fund on the NHS – however, in the future, treating only the patients that will benefit from certain treatments will save the NHS money in the long term.”
Dr Lesley Walker, Cancer Research UK’s director of cancer information, said: “Health professionals may in the future be able to use this information to direct treatment to patients most likely to benefit and avoid giving treatment that is less likely to be effective to patients with drug resistant cancers.
“Ultimately similar approaches could reduce the cost of delivering cancer care whilst enabling improved patient access to beneficial treatments.”
The scientists used a technique called RNA interference to screen the genes. It involves turning genes on or off by targeting the molecules that carry their coded instructions.