THURSDAY, Jan. 25 (HealthDay News) -- Men who have breast cancer have a significantly increased risk of a second cancer, according to the largest study ever done on the subject.

"We looked at the risk not only of a second breast cancer but also of other cancers. We found the risk of other cancers increased as well," said lead researcher Hoda Anton-Culver, director of epidemiology at the University of California at Irvine.

Her team published its findings in the February issue of Breast Cancer Research.

Breast cancer remains rare among men. Only about 1 percent of breast cancers are diagnosed in men, but some 1,400 new cases are reported in the United States each year, according to the American Cancer Society.

Because of the relatively small incidence of male breast cancer, "not one study until now has looked at large numbers," Anton-Culver said. However, "our study looks at a very large number of men," she said, "so there can be validity to large numbers of a rare cancer like this one."

The researchers analyzed data from the California Cancer Registry on 1,926 men who developed breast cancer from 1988 to 2003.

Of these, 221, or 11.5 percent, went on to develop a second cancer at least two months after their breast cancer diagnosis.

One significant second cancer in the group was malignant melanoma, with an incidence that was 50 percent higher than normal, she said. There was also an elevated risk of stomach cancer.

There are several possible explanations for the increased risk, Anton-Culver said. It might be due to the side effects of treatment of the primary breast cancer, for example. But the most probable cause is genetics, she said, with the men being at "higher risk of developing cancer in general."

And studies by the group have shown a high incidence of a breast cancer-related gene, BRCA2, in the men, Anton-Culver said.

The findings could have a very practical application in terms of screening, she said. Her group has been collecting family histories of men with breast cancer, in collaboration with British researchers.

"We definitely do see an association between breast cancer in men and an increased risk of being a carrier of a cancer-related gene," Anton-Culver said. That relationship indicates that a screening program looking at close relatives of men with breast cancer could help with the early detection of malignancies, she said.

"Once you have a man with breast cancer, you have a great target for screening," Anton-Culver said.

More information

For more on male breast cancer, go to the U.S. National Library of Medicine.