Findings from the new research suggest the causes of the disease may differ between women and men.
Around 350 men in the UK are diagnosed with the disease each year, compared with 48,000 women. It was already known the faulty BRCA2 genes are involved in around 10% of cases, a higher proportion than among women.
Changes in the RAD51B gene – which is involved in the repair of damaged DNA – also play a role, according to the research. They increase the risk of male breast cancer by up to 50%.
Dr Nick Orr, from the Breakthrough Breast Cancer Research Centre at the Institute of Cancer Research in London, said: "It shows that while there are similarities with female breast cancer, the causes of the disease can work differently in men. This raises the possibility of different ways to treat the disease specifically for men."
Dr Orr led the research reported today in the journal Nature Genetics. A team of international scientists screened the genetic code of 823 male breast cancer patients and investigated 447,000 alterations in their DNA.
The study highlighted RAD51B, which when faulty also raises the risk of breast cancer in women. However, different parts of the gene are implicated in men's and women's cancers.