Men with naturally high levels of the female hormone oestrogen may have a greater risk of developing breast cancer, according to research by an international collaboration including Cancer Research UK published today in the Journal of Clinical Oncology.
This is the first time a link between oestrogen levels in the blood and male breast cancer has been identified, despite its connection to breast, womb and ovarian cancers in women.
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.
Male breast cancer is very rare with one man in every 100,000 diagnosed with breast cancer 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.
Mark Cross, 46, a police officer from Cambridgeshire, was diagnosed with breast cancer in 2009. He had a mastectomy and then follow-up treatment of chemotherapy and radiotherapy. His treatment ended in September 2010. He said: "The police sometimes get a bit of a reputation for being macho but I had great support from everyone within the Metropolitan police service. Not many people know that men get breast cancer too and it was a complete surprise to be diagnosed. My advice to all men is if you develop a lump on your chest - or anywhere else on your body - get it checked by your doctor as soon as possible. I hope my experience will raise awareness for other 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."