Men with the highest levels of oestrogen were two and a half times more likely to develop breast cancer than men with the lowest levels of the hormone, a study published in the Journal of Clinical Oncology said.
While male breast cancer is rare, it still affects one man in every 100,000 diagnosed each year in the UK. Around 350 male cases are diagnosed each year in the UK compared with nearly 50,000 cases of breast cancer in women.
The research at the National Cancer Institute in the United States was part of an international collaboration between Cancer Research UK, the National Cancer Institute and others.
The aim was to study a large international pool of men with breast cancer. The research compared oestrogen levels in 101 men who went on to develop breast cancer with 217 healthy men.
Study author Professor Tim Key, Cancer Research UK’s hormone and nutrition expert at the University of Oxford, said: “We’ve shown for the first time that just like some forms of the cancer in women, oestrogen has a big role to play in male breast cancer. So now the challenge is to find out exactly what this hormone is doing to trigger this rare form of the disease in men, and why some men have higher levels of oestrogen in their blood. Our discovery is a crucial step forward in understanding the factors behind male breast cancer.”
The symptoms, diagnosis and treatment of male breast cancer are very similar to breast cancer in women. The main risk of developing the disease in men is age and almost eight in 10 cases are diagnosed in those aged 60 and older.
Dr Julie Sharp, head of health information at Cancer Research UK, said: “Breast cancer in men isn’t discussed very often, so a diagnosis can be a big shock for the small group of men who develop the disease.
“Some of the oestrogen variation in men will simply be natural, but for others there may be a link to being overweight. Fat cells in the body are thought to drive up the body’s level of this hormone in men and women, so this is another good reason to try and keep a healthy weight.
“This early research is crucial in understanding why these men get breast cancer - so that one day we can treat it more effectively.”