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Dec. 14, 2006 (San Antonio) -- A virus that infects the common house mouse may cause more than one in three cases of breast cancerbreast cancer in the U.S., researchers report.
In Asia, however, the virus plays a very small role in causing the disease, says James F. Holland, MD, distinguished professor of neoplastic diseases at Mt. Sinai School of Medicine in New York.
"The human breast cancercancer virus may explain why breast cancer rates differ throughout the world," he tells WebMD.
Holland reviewed recent research on the breast cancer virus at the San Antonio Breast Cancer Symposium.
How Breast Cancer Virus Spreads
Holland says the virus does not appear to be inherited from one's parents. Rather it is spread from person to person, like the common cold.
That conclusion came from a study of more than 200 women with breast cancer. Researchers detected the virus in about 30% of tissue samples from their affected breast, but in only one sample of normal tissue from the unaffected breast.
"If it was genetically transmitted, the virus would be present in both tissue samples," Holland explains.
Michael Dosik, MD, a breast cancer specialist at Stony Brook University in Stony Brook, NY, says that "while interesting, there's still a long way to go."
"While the virus seems to be spread from person to person -- not genetically -- we need to figure out exactly how it is transmitted," he tells WebMD.
Holland agrees. "It could be spread by sneezing or perhaps eating infected food, for example. We're testing many theories."
Viruses and Breast Cancer
Viruses are known to be involved in the development of several cancers, including cervical cancercervical cancer; previous studies suggested that a virus similar to the mouse mammary tumor virus (MMTV) is associated with breast cancer in humans.
Holland says that other new research suggests that the human breast cancer virus is "a kissing cousin" of MMTV, "most likely caused by a mutation that occurred thousands of years ago."
Other new work suggests that variations in breast cancer prevalence worldwide can be explained by the fact that the species of house mouse that carries that virus is more common in certain regions, he says.
In North America, Europe, and Australia, where the species is common, the virus was detected in 30% to 40% of breast cancer tissue samples, he says.
In Asia, where the species in rare, the picture is quite different. In Japan, only 12% of samples were infected. In Vietnam, less than 1% of samples tested positive.
In that study, researchers tested 524 tissue samples from women treated for breast cancer in the U.S. and compared the results with breast cancer tumor samples from women treated for breast cancer in other countries.
SOURCES: San Antonio Breast Cancer Symposium, Dec. 14-17, 2006. James F. Holland, MD, distinguished professor of neoplastic diseases, Mt. Sinai School of Medicine, New York. Michael Dosik, MD, Stony Brook University, New York.