The rate of male breast cancer is on the rise and the disease in men is usually detected when the tumours are bigger, have spread and may be more aggressive, compared to diagnosis of the disease in women, concludes the largest study ever conducted of male breast cancer.

The findings, published in the online edition CANCER and will appear in the July 1 print issue of the publication, suggest both that breast cancer in men may have some important biological differences from the female disease, and that men are seemingly less aware than they should be that they can develop breast cancer.

According to the study's lead investigator, Sharon H. Giordano, M.D., assistant professor in the Department of Breast Medical Oncology at The University of Texas M. D. Anderson Cancer Center, the incidence of the disease has increased significantly in the last 25 years, from 0.86 to 1.08 per 100,000 men.

"Male breast cancer is rare, accounting for less than one percent of all breast cancer, or about 1,600 new cases in the United States in 2004. While, it's not as high of an increase in cases as that in women, men should be alert to the possibility that the disease could affect them," says Giordano.

Because breast cancer in men is rare, little is known about how it differs from breast cancer in women and how it should be best treated. To assess dissimilarity, Giordano and her M. D. Anderson colleagues used information from a National Cancer Institute database called SEER (Surveillance, Epidemiology, and End Results), which is the authoritative source of information on cancer incidence and survival in the United States.

They analyzed SEER data from 1973 through 1998 on 2,524 cases of male breast cancer and 380,856 cases of female breast cancer. Compared to female patients, the investigators found that male patients were significantly older when 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.

"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," says Giordano.

One reason for such a late diagnosis may be that men assume they are experiencing a benign condition called gynecomastia, or atypical growth of breast tissue that affects about a third of males at some point in their lives, says Giordano. The condition, common in adolescent boys, can come and go over a man's lifetime and "men may think new growth of breast tissue is just another occurrence of this condition," she explains.

Furthermore, Giordano and the researchers found that the most common types of cancers in men were invasive ductal carcinoma, found in 93.4 percent of the men, and papillary carcinoma, which accounted for 2.6 percent of the cases.

Yet despite these differences, five-year, 10-year and median survival were not different between men and women, investigators say.

Also of interest to the researchers was the finding that male patients are more likely than female patients to have estrogen receptor-positive tumours.

"We are not sure why this is so, but it may indicate some important differences in tumour biology," she says. "In addition, this implies that use of tamoxifen in men may be as beneficial as it is to many women," says Giordano.

"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," she says.