There may be a link between breast cancer and bovine leukemia virus, according to new a study published in PLOS ONE.
Researchers from UC Berkeley in California analyzed breast tissue from 239 women for presence of the cattle virus, comparing samples between women who had breast cancer and those who had no history of the disease. Of the samples from women with breast cancer, 59 percent showed evidence of bovine leukemia virus exposure compared to only 29 percent from the tissues of women who had never had cancer.
"The association between BLV infection and breast cancer was surprising to many previous reviewers of the study, but it's important to note that our results do not prove that the virus causes cancer," Gertrude Buehring, a professor of virology in the Division of Infectious Diseases and Vaccinology at UC Berkeley's School of Public Health, lead author of the study, said in a statement. "However, this is the most important first step. We still need to confirm that the infection with the virus happened before, not after, breast cancer developed, and if so, how."
In 2007, the U.S. Department of Agriculture found that all dairy operations with cattle herds numbering more than 500 had tanks of bulk milk that tested positive for the virus. Dairy operations with smaller herds, fewer than 100 cattle, still tested positive 83 percent of the time.
The virus causes deaths in only 5 percent of infected animals, and while there is some evidence for viruses being cancer-causing, these results are correlative and do not indicate the virus' role in breast cancer, according to the authors.