Existing drugs could benefit one in five breast cancer patients

A genetic study of breast cancer patients suggests that existing drugs developed for treating rare breast and ovarian cancers may help more patients than previously thought.

The researchers predict that up to 20 percent of breast-cancer patients may benefit from treatment with a class of drugs known as PARP inhibitors. These drugs were previously only thought to work in the one to five percent of breast and ovarian cancer patients who have inherited mutations in the BRCA1 or BRCA2 genes.

Other cancers may, and often do, have spontaneous mutations (non-inherited) in these genes, potentially rendering them sensitive to PARP inhibitors, but these BRCA1/2-deficient cancers are very hard to identify.

An international team led by the Wellcome Trust Sanger Institute in Cambridge developed a computer-based, method to identify cancers lacking a functional BRCA1/2. In a cohort of 560 breast cancer patients, they found that around 22 percent were BRCA1/2 deficient, meaning that they might benefit from PARP-inhibitor treatments.

'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,' said lead researcher Dr Serena Nik-Zainal. 'This could change how clinical trials are designed in the future,' she added.

The research relies on advances in DNA sequencing technology and on complex computational analysis. The genomes of the tumours belonging to the study participants were sequenced and compared, using a specially developed algorithm known as HRDetect, with those of patients with known BRCA1/2 deficiency.

'Crucially, this study is an early but encouraging step towards being able to offer women treatments targeted to the genetic make-up of their breast cancer,' Baroness Delyth Morgan, chief executive of the charity Breast Cancer Now, told The Independent.

It remains to be tested in clinical trials whether PARP inhibitors can actually benefit this larger group of cancer patients – so far, the research is purely theoretical. Professor Mike Stratton, director of the Sanger Institute, said: 'To translate these results into treatments, further sequencing of cancer genomes and more clinical trials are urgently needed, but this is a most promising start.'