Researchers in a new study found that a significant number of breast cancer cells from more than 200 women had evidence of exposure to bovine leukemia virus, or BLV. BLV infects dairy and beef cattle’s blood cells and mammary tissues, and was for a long time thought not to be able to infect humans.
Nearly all bulk milk tanks at large factory farms are infected with BLV, but only about five per cent of cows get sick if they have the virus, according to the US Department of Agriculture. The same group of researchers at the University of California Berkeley involved in the new study also found last year that BLV could be transmitted to humans.
“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,” said Dr Gertrude Buehring, a professor of virology in the University of California Berkeley, in a press release.
“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,” Buehring said.
Using donated tissue from the Cooperative Human Tissue Network, the researchers compared breast tissue from 239 women who either had breast cancer or did not.
They found that 59 per cent of breast cancer cells had evidence of exposure to BLV based on the presence of viral DNA in the cells. Cells from women who had not had breast cancer only had evidence of exposure 29 per cent of the time.
When researchers further analysed the data, they found the risk of developing breast cancer was 3.1 times higher if BLV was present in a woman than if it was not. Buehring said the odds ratio is higher than other well known risk factors for breast cancer, including obesity, alcohol consumption and hormones.
