09/21/2015 12:18 EDT | Updated 09/20/2016 05:12 EDT

Does Breast Cancer Have a Connection to Cows?

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Cancer is the number one killer in this country. In women, breast cancer is the second leading cause of this potentially deadly disease. Researchers across the country and around the world are working tirelessly not only to find a cure but also to find the cause.

When it comes to how exactly breast cancer is triggered, the answer is elusive. Research has shown exposure to high levels of estrogens plays an important role. One particular estrogen culprit, known as 17β-estradiol, has been given extra consideration as it is the most active hormone in breast tissue. About 70 per cent of breast cancers are linked to this one molecule.

About 10 per cent of cases rise from environmental factors. These include exposure to UV radiation and pollution, including cigarette smoke. Avoidance of these agents has since become a priority for public health officials to prevent all types of cancer, including breast.

As for that other 20 per cent, it most likely comes from some type of microbial infection, particularly viral. For 50 years, microbiologists have stressed these small pathogens play an important role in the development of cancer. Several cancer-causing species have been found such as hepatitis B virus, Epstein-Barr virus (also known as the kissing disease), and human papillomavirus, which we all know as HPV.

But here lies a problem. Although viruses can indeed cause cancer, there has been no confirmed link between any microbial invader and breast cancer. Many have been proposed yet there has been no conclusive evidence to suggest this particular form of cancer has a microbiological link.

That may now change thanks to a study released earlier this month by an American team of researchers. They have found a high association between exposure to a virus and the onset of breast cancer. But there's a twist. This isn't a human virus; it comes from cows.

It's called Bovine Leukemia Virus, or BLV. It's been known since the 1960s as the cause of blood cancer in the bovine population. In these animals, BLV is rampant with up to 100 per cent of some dairy herds infected although only about 5 per cent end up with leukemia. Still, it is an important pathogen with the potential to cause significant harm. The virus isn't limited to cows. It has been found to affect other animal species including sheep and rabbits and can be quite deadly.

The same cannot be said for humans. We do get infected but there are no symptoms. The virus seems to get inside us and either die or travel around looking for a nice place to colonize. On the surface, this may seem harmless but research has learned the effects of BLV infection could be far worse than imagined.

The first hints the virus could cause troubles happened about ten years ago when traces of the virus' genetic material was found in people suffering from leukemia and lung cancer. The data wasn't entirely convincing, however, but the caution flag was raised. For anyone looking at the cause for human cancers, they may find a cow virus.

Little progress was made on this front until last year, when some of the same authors of this new study found BLV in breast tissue. Although the finding wasn't entirely a shock, the results did suggest more research needed to be done to determine if there was any link to breast cancer.

To achieve this goal, the authors decided to look at breast tissue taken from women who had undergone mastectomies for breast cancer. As a control, they took breast tissue from healthy women undergoing reduction surgery. In total, the group looked at 218 breast samples, 114 with cancer and 104 controls.

The tissues were taken back to the lab and investigated for any signs of BLV. If they were right, there would be a higher number of cancerous tissues containing the virus. They were not disappointed. In total, 59 per cent of cancerous tissue contained BLV. In the controls, that number was only 29 per cent. This represented a 30 per cent difference. When computed into risk, the authors revealed the risk for cancer was three times higher if BLV was in the tissue.

For the authors, this result offered a significant step in understanding the role of BLV in breast cancer. They even went as far to suggest the 29 per cent of controls who had the virus may be at a greater risk for the disease later in life. Much like HPV, BLV can take decades to transform cells into cancer.

The authors did not, however, suggest all women should be tested for BLV. Although the results were significant and striking, they did not want to change the current landscape before more studies are performed. While their study is definitely an eye-opener, they admitted this was merely the beginning and more work needed to be done in the lab and also on the farm. After all, BLV had to somehow come from cows. Unfortunately, no one quite knows yet how that happens.


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