Case-Control Study Examines Bovine Virus Contribution to Breast Cancer Risk
A case-control study has reportedly identified a “significant” association
between bovine leukemia virus (BLV) infection and human breast cancer.
Gertrude Case Buehring, et al., “Exposure to Bovine Leukemia Virus
Is Associated with Breast Cancer: A Case-Control Study,” PLoS One,
September 2015. After analyzing breast tissue specimens obtained from
239 donors for the presence of BLV, University of California, Berkeley,
researchers apparently detected BLV “in the mammary epithelium of
59% of women diagnosed with breast cancer versus 29% of those with no
history of breast cancer.” They further suggest that “as many as 37% of
breast cancer cases may be attributable to BLV exposure,” with an odds
ratio “comparable to that of commonly cited reproductive, hormone, and
lifestyle risk factors for non-hereditary (sporadic) breast cancer.”
As explained in a concurrent press release, a 2014 study published
in Emerging Infectious Diseases confirmed the presence of BLV in
humans, though it is currently unknown how the virus passes between
species. The study hypothesizes that possible transmission routes could
include undercooked beef or raw cow’s milk, but there may also be a
longstanding BLV reservoir in the human population due to millennia of
cattle domestication.
The researchers note, however, that this case-control study does not
prove the virus causes cancer. As the lead author elaborates, “We still
need to confirm that the infection with the virus happened before, not after, breast cancer developed, and if so, how… Studies done in the 1970s
failed to detect evidence of human infection with BLV. 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. As a result, there has
been little incentive for the cattle industry to set up procedures to contain
the spread of the virus.” See UC Berkeley Press Release, September 15,
2015.
Issue 578
