If a man carries a faulty gene, new research opines that he then has a one in 15 chance of developing breast cancer by the time he hits age 70.
A faulty copy of the gene - called BRCA2 - can be passed on to both sexes through the generations.
Now, scientists have worked out the lifetime risk of breast cancer for men who carry the faulty gene in the largest study of its kind.
Among the families, 16 men who were first degree relatives of known BRCA2 carriers had developed breast cancer between the ages of 29 and 79. Another eight cases occurred in second degree relatives.
Study's lead author Professor Gareth Evans, from St Mary's Hospital in Manchester, said that the vast majority of the men who developed breast cancer were BRCA2 fault carriers themselves.
Analysis showed the risk of breast cancer among men with a faulty BRCA2 gene was 7.1 percent by the age of 70 and 8.4 percent by the age of 80.
"There is a one in 1,000 chance of developing breast cancer as a man in the general population," the Independent quoted Evans as saying.
"Men don't have to have a faulty copy of BRCA2 to get breast cancer, but the highest risk for man is if they have a faulty copy of the gene.
"The risk is 90 times higher than the risk for men in the general population," Evans added.
The study has been published in the Journal of Medical Genetics.