Study: Virus in Cattle Linked to Increased Risk of Breast Cancer
Risk '3.1 times higher' if BLV was found
Researchers from UC Berkeley have discovered a link between leukemia in cows and breast cancer.
Scientists found that a significant number of breast cancer cells in women with breast cancer showed evidence of exposure to bovine leukemia virus, or BLV. The researchers say the odds of someone developing breast cancer are far higher in those exposed to BLV than with other common risk factors associated with breast cancer, including obesity, alcohol consumption and the use of postmenopausal hormones. 
For the study, published in this month’s issue of PLOS One, researchers analyzed breast tissue from 239 women for the presence of BLV. The team compared samples from women with breast cancer to women who had no history of the disease. Fifty-nine percent of the breast cancer samples showed evidence of exposure to BLV viral DNA. Cells from women who had not had breast cancer showed evidence of the virus only 29% of the time. 
Additionally, upon further analysis, the researchers determined the risk of developing breast cancer was 3.1 times higher if BLV was found.
“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,” says study lead author Gertrude Buehring, a professor of virology in the Division of Infectious Diseases and Vaccinology at UC Berkeley’s School of Public Health.
“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.”
But if further research does prove that BLV can cause breast cancer, it would not be the first time a virus was linked to the development of cancer; liver cancer can be caused by hepatitis B and C, for example, and human papilloma virus is known to be a cause of cervical and anal cancer.
BLV is found in infected dairy and beef cattle’s blood cells and mammary tissue. It can be transmitted between cattle through infected blood and milk, but only sickens less than 5% of the animals.
The retrovirus is present in nearly all bulk milk tanks at large factory farms. For years, it was believed that BLV could not be transmitted to humans, but the same group of UC Berkeley researchers discovered last year that it could, indeed, be passed to people.
In 1996, the first U.S. study of BLV revealed that 89% of U.S. dairy operations had the virus.
A 2007 U.S. Department of Agriculture survey of bulk milk tanks found that 100% of dairy farms with herds of 500 or more cows tested positive for BLV antibodies. Dairy operations with 100 or fewer cows per herd tested positive 83% of the time.
“The tests we have now are more sensitive, but it was still hard to overturn the established dogma that BLV was not transmissible to humans, says Prof. Buehring.”As a result, there has been little incentive for the cattle industry to set up procedures to contain the spread of the virus.”
The research doesn’t show how BLV infects breast tissue, but Prof. Buehring says the virus could spread to humans through unpasteurized milk, uncooked meat, or human-to-human transmission. She also notes that further research is needed to determine if the virus is present in breast tissue before cancers form. 
 Berkeley News
Julie Fidler is a freelance writer, legal blogger, and the author of Adventures in Holy Matrimony: For Better or the Absolute Worst. She lives in Pennsylvania with her husband and two ridiculously spoiled cats. She occasionally pontificates on her blog.