PARP inhibitors could be used to treat many more women with breast cancer than at present, according to British experts.
The drugs are used to treat women with the BRCA1 or BRCA2 mutations.
But, according to findings at the Wellcome Trust Sanger Institute, Cambridge, UK, many other breast cancers are genetically similar and may be treatable with PARP inhibitors.
Their analysis, published last night, suggests the drugs could be used to treat up to 20% of patients with breast cancer. No more than 5% of cases are linked to the BRCA1 and BRCA2 genes.
The findings, reported in Nature Medicine, involved an analysis of the genomes of 560 patients and the study of "every single type of mutation possible," the researchers say.
They found that many patients had mutational signatures identical to those of the faulty BRCA1 and BRCA2 genes – even though the patients had not inherited these mutations.
Researcher Dr Serena Nik-Zainal said: "In the past, clinical trials for PARP inhibitors have focused mainly on the one to 5% of women with breast cancer. However, our study shows that there are many more people who have cancers that look like they have the same signatures and same weakness as patients with faulty BRCA1 and BRCA2 genes.
"We should explore if they could also benefit from PARP inhibitors."
She added: "The results suggest that clinical trials now need to look at cancer patients who share the same genetic signature in their cancer. This could change how clinical trials are designed in the future."
Fellow researcher Dr Helen Davies said: "Further work needs to be done as there could be tumours with the same mutational signature elsewhere in the body that may respond to these drugs.”
Helen Davies et al. HRDetect is a predictor of BRCA1 and BRCA2 deficiency based on mutational signatures. Nature Medicine 13 March 2017; doi: 10.1038/nm.4292
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