The study, the biggest of its kind, improves the chances of getting drugs that, like a sniper's rifle, aim at a specific type of tumour, they said.
Researchers led by Fabrice Andre, a professor at the Gustave Roussy Institute in Paris, unravelled the DNA of cancer cells found in more than 407 women whose breast cancer had spread dangerously to other tissues.
The goal was to pinpoint genes linked with specific types of tumour, and see if these could be matched to new, experimental drugs that were already in the test pipeline.
The probe found that nearly half of the patients -- 46 per cent -- did have tumours whose genetic profile offered a potential target for drugs.
Of these, 43 were then enrolled in clinical trials for new drugs corresponding to this profile.
Thirteen of them responded to treatment.
"Until now, genetic testing has only analysed a limited number of genes to select which targeted drugs are suitable for individual patients and many treatment opportunities may be missed," explained Andre.
The study is reported in a specialist journal, The Lancet Oncology.
