Scientists find five times more genes linked to breast cancer than were previously known

A major international study on the genetics of breast cancer published in Nature Genetics has identified more than 350 genetic variants that increase a person's risk of developing the disease.

The researchers, from over 450 departments and institutions worldwide, say the findings will help provide the most detailed picture yet of how differences in our DNA put some women at greater risk than others of developing breast cancer.

'This incredible haul of newly-discovered breast cancer genes provides us with many more genes to work on, most of which have not been studied before,' said co-author Dr Alison Dunning from the University of Cambridge. 'It will help us build up a much more detailed picture of how breast cancer arises and develops. But the sheer number of genes now known to play a role emphasises how complex the disease is.'

Breast cancer is a polygenic disease, meaning no single genetic variant or gene causes the disease, instead it is a combination of a number of genetic variants that act together to increase the likelihood of developing the disease.

In this new study, researchers collaborated to compare the DNA of 110,000 breast cancer patients against that of 90,000 healthy patient controls. The large sample allowed them to identify 352 genetic variants that are associated with an increased risk of breast cancer. It is not yet clear exactly how many genes these variants affect, but the researchers have identified 191 genes with reasonable confidence, with less than one in five of these being previously recognised.

Previous genome-wide association studies, which also compared the DNA of patients against that of healthy controls, had identified 150 regions of the genome that clearly affect breast cancer risk as well as changes within these regions that affect the risk of developing cancer. Yet the researchers of this latest study point to the importance of identifying the specific variants or genes involved. 

'We know from previous studies that variants across our DNA contribute towards breast cancer risk, but only rarely have scientists been able to identify exactly which genes are involved,' said co-author Dr Laura Fachal, of the University of Cambridge. 'We need this information as it gives us a better clue to what is driving the disease and hence how we might treat or even prevent it.'

Of the newly discovered genetic variants, a third predispose women towards developing hormone-responsive breast cancer: the type affecting four out of five breast cancer patients, which responds to hormonal treatments such as tamoxifen. Fifteen percent of the genetic variants predispose women to the rarer type, oestrogen-receptor-negative breast cancer, with the remaining genetic variants playing a role in both types.

Furthering our understanding of the genetic risk of developing breast cancer will allow doctors and clinicians to provide advice on the best treatment strategy for both reducing a person's risk and also preventing the onset of the disease.