Male breast cancer linked to obesity
Other risk factors include enlarged male breasts, and having an extra X chromosome besides the one men normally inherit from their mothers.
Around 100 men are diagnosed with breast cancer each year in Australia and about 400 each year in the UK, but the causes of male breast cancer are poorly understood.
The UK's Male Breast Cancer Pooling Project gathered together data on the disease from studies conducted around the world.
It found that obesity, and several other physical and hormone-related traits, were associated with increased breast cancer risk in men.
The results published in the Journal of the National Cancer Institute (JNCI) showed that breast cancer risk in men increases with weight.
Clinical obesity, defined by having a BMI of 30 or above, increased the chances of a man developing breast cancer by around 30%.
An association was also seen with gynecomastia, enlarged breast tissue in men, which appeared to be