TUESDAY, July 13, 2004 (HealthDayNews) -- A virus similar to one known to cause breast cancer in mice may also play a role in the development of human breast cancer, according to a new study that may re-ignite a long-running debate.
The study, appearing in the July 12 issue of Cancer online, provides "more evidence that a virus may play a role in breast cancer," said Dr. Paul H. Levine, a research professor of epidemiology and biostatistics at George Washington School of Public Health and Health Services in Washington, D.C., and the study's lead author.
Even so, "there is evidence that it's not a very contagious virus, if it is a virus. And it may explain [only] a relatively small percent of breast cancers," he added.
"As early as the late 1930s, researchers have talked about the idea of a virus contributing to breast cancer," Levine said.
In the current study, Levine and his colleagues also found geographic differences, with evidence of the mouse-like viruses more prevalent in human breast cancer samples taken from Tunisia than those from other countries.
Seventy-four percent of the 38 samples taken from Tunisian tumors for the current study tested positive for a genetic sequence similar to the MMTV virus, which causes breast cancer in mice. Tumors from other countries tested positive less frequently -- 36 percent of U.S. tumor specimens, 38 percent of those from Italy, 42 percent from Australia, and 31 percent from Argentina.
What was found, Levine said, is "a viral footprint suggesting there is a virus like MMTV. "
"This is the first study that shows differences in international patterns," Levine said. "In the study, we had two labs independently looking at samples -- Mount Sinai and the National Cancer Institute." Each got the same results for the same cases, he said.
But Levine also put the research in perspective. "This does not explain the etiology of the vast majority of breast cancer cases in the world, especially in the U.S.," he said.
"We don't know the exact role [of the virus-like agent]," he said. It could be a trigger or an important contributing factor, he said.
The MMTV virus may be spread by a species of house mouse that is very common in North Africa but not so common in the U.S., the authors said. Some studies show some colonies of these mice are commonly infected with MMTV.
The team also found that 89 percent of the MMTV-positive samples were from tumors that were very aggressive.
"It's important to look at this further," said Dr. Herman Kattlove, medical editor for the American Cancer Society, who notes that viruses have been found to be related to some cancers, such as that of the cervix. But the Cancer study is preliminary, he said. "My sense is we don't know what this means. We don't know that [the virus-like sequence] has anything to do with the cause of the cancer just from this study."
"It's very interesting, but at this point it seems to be a bit of a reach," added Dr. Dennis Holmes, assistant clinical professor of surgery at the University of Southern California's Keck School of Medicine. Like Kattlove, he called for more research.
Learn about breast cancer and its treatment from the American Cancer Society.