More men are developing breast cancer - but most fail to spot tumours until they are at an advanced stage, a study has warned.
Breast cancer is usually thought of as a 'woman's disease'
University of Texas research found that, while men are far less likely to develop breast tumours than women, the numbers are increasing.
Writing in an online edition of the journal Cancer, they warn men seem to be unaware they can develop the cancer.
UK experts said the cancer was rare, but men should be aware of changes.
The researchers looked at a National Cancer Institute data on cancer incidence and survival in the US from 1973 to 1998.
They found that, over the last 20 years, the incidence of male breast cancer had increased from 0.86 to 1.08 per 100,000 men.
They then examined 2,524 cases of male breast cancer and 380,856 cases of female breast cancer on the database, diagnosed over that period.
The researchers found that compared to female patients, men tended to be significantly older when they were diagnosed - 67 years versus 62 years of age.
They were also more likely to have later stage disease and had more spread of the cancer to their lymph nodes.
'Easier to spot'
Professor Sharon Giordano, who led the research, said: "Male breast cancer is rare, accounting for less than one per cent of all breast cancer."
But she said: "Men should be alert to the possibility that the disease could affect them."
Professor Giordano added: "It's perhaps ironic that tumours in men are easier to feel than they are in women, yet the disease is being discovered at a later stage in men than in women."
The researchers say that part of the reason for late diagnosis may be that men assume they are experiencing a benign condition called gynecomastia, or breast tissue growth, that affects about a third of males at some point in their lives.
The condition, which is common in teenage boys, can come and go over a man's lifetime.
Professor Giordano said: "Men may think new growth of breast tissue is just another occurrence of this condition."
The team also found that men often had more larger tumours which had spread further and more aggressive forms of cancer when they were diagnosed.
However, survival rates for men and women were no different.
The researchers said men were more likely than women to have oestrogen-positive tumours.
Professor Giordano: "We are not sure why this is so, but it may indicate some important differences in tumour biology.
"In addition, this implies that use of tamoxifen in men may be as beneficial as it is to many women."
She added: "Now that we have a clearer understanding of the biology of breast cancer in men, further research is needed to determine the optimal treatment for men."
'Campaigns aimed at women'
Henry Scowcroft, Science Information Officer at Cancer Research UK said: "Breast cancer is very rare among UK men, and when it does occur, it tends to do so between the ages of 60 and 70.
"Only about 300 men are diagnosed with the disease each year, compared with about 41,000 new cases in women. Because of this, most breast cancer awareness campaigns are aimed at women.
"While Cancer Research UK does not recommend that men, especially young men, examine themselves regularly, it is important to visit your GP straight away if you notice any change in your body that is not normal."