A link between bacteria and breast cancer?

In just about every nook, cranny and crevasse of the human body, bacteria can be found, affecting all aspects of our health. They outnumber our human cells by ten-to-one, and would fill a big soup can if we could somehow slough them off. Still, it comes as a surprise that bacteria thrive even inside human breast tissue, an area “traditionally thought of as sterile,” says PhD student Camilla Urbaniak of Western University, lead author of a new study published online today. More intriguing, women undergoing breast cancer treatment seem to have different populations of bacteria in their breasts than those who are cancer-free. This suggests that bacteria could play a role in how the disease progresses, and maybe one day, how it’s treated.

Urbaniak’s study looked at 81 women with and without cancer, in Canada and Ireland, aged 18 to 90. (Some were having benign or cancerous tumours removed; others were undergoing breast reduction surgery.) Although it’s well-established that human breast milk is chock-full of bacteria, some of these women had never given birth or lactated, and they still had plenty of bacteria inside their breast tissue. “In all the samples we collected, from as close to the nipple to as far back as the chest wall, we found diverse populations,” Urbaniak says. So how did bacteria get in there? “We don’t know, and we want to find out.” The populations seen in the breast were the same ones typically found in the gut, mouth, nasal passages, and on the skin. Women with cancer had different dominant types than those who were healthy; in their cases, bacteria thrived in and around the tumour.

This is the first study of its kind, so there are lots of questions. Urbaniak hopes to keep exploring how different types of bacteria might contribute to cancer, or help ward it off. In the future, antibiotics could be used to manipulate this “breast microbiome,” as she and her collaborators call it. But antibiotics have a major disadvantage: they nuke both dangerous and protective bacteria alike. Urbaniak thinks that probiotics, a tailor-made dose of live bacteria that confer health benefits, might be a better option. “It’s too soon to tell,” she says, “but probiotic therapies might be useful treatment.” (Other Canadian teams are exploring doses of beneficial bacteria for various conditions, like deadly C. difficile infection, for example.)

If it’s one day confirmed that bacteria play a role in breast cancer, this won’t come as a total shock. By now, studies have linked certain types of bacteria to colon cancer, gastric cancer, and oral cancer, to name a few. “But it’s not just cancer,” Urbaniak says. “From an early age, if you don’t have a ‘normal’ bacterial population, it can lead to inflammatory bowel disease, diabetes, allergies,” and a host of other problems. The bacteria that co-exist with us are hugely influenced by everything from what we eat, to the medicines we take, she says. “People don’t realize how important they are. We need to be careful we’re not causing a shift in these bacterial populations,” or we could be meddling with our health in ways we still don’t understand.