Breast cancer cells from more that 200 women were found to contain evidence of exposure to bovine leukemia virus (BLV), according to a new study released and cited on upi.com.

Dr. Gertrude Buehring, a professor of virology in the University of California Berkeley, said in a press release “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.”

Dr. Buehring added this was an important first step, but research still had to confirm that the exposure to the virus happened before the breast cancer developed and not after the cancer began to grow.

The researchers compared the breast tissue of 239 women, some with and some without breast cancer.  The tissue was donated from the Cooperative Human Tissue Network.

Based on the presence of viral DNA in the cells, fifty nine percent of the cells from subjects with breast cancer had evidence of exposure to BLV, while only twenty nine percent of the subjects without cancer showed they had been exposed to BLV.

Further analysis found that the risk in developing breast cancer was 3.1 times greater with the presence of BLV than without.  Buehring noted that was higher that other identified contributing factors, such as obesity, alcohol consumption and hormones.

Buehring pointed out the study did not prove that BLV caused breast cancer, but noted it would not be the first virus that could be shown to cause cancer.  Hepatitus B virus has been shown to cause liver cancer, and human papillomavirus can cause cervical and anal cancer.

Almost all bulk milk tanks are infected with BLV.  But, according to the U.S. Department of Agriculture, only 5 percent of cows get sick when they have the virus.  The same researchers at UC-Berkeley were involved in a study last year that determined BLV could be transmitted to humans.