Breast Cancer and Metastases: Is Dysbiosis a Factor?

Yesterday, I read an article[i] in the University of Virginia’s online newspaper about the work of a team of their scientists and graduate students that I thought worth sharing with you.  The paper[ii] was just published in the journal, Cancer Research, and while it was conducted in an animal model, the findings are still very interesting and potentially very important.

First a fact:  the most common type of breast cancer, about 2/3rds of cases in fact, is called hormone receptor positive (HR+).  So, using a mouse model of this type:  for two weeks, the experimental group of mice were given non-absorbed antibiotics (that stay in the gut), wiping out much of their gut bacteria, while the control group was given water.  All the mice were then injected with breast cancer tumor cells.

They found that the mice given the antibiotics had “…enhanced tumor cell dissemination to lymph nodes, lungs, and peripheral blood at both early and advanced timepoints after tumor initiation.” That is, the cancer metastasized much more readily than in the control group.  They found too that dysbiosis “…promoted early inflammation within the mammary gland….”

Dr. Melanie Rutkowsi, lead author of the paper, is quoted as saying, “In this inflamed environment, tumor cells were much more able to disseminate from the tissue into the blood and to the lungs, which is a major site for hormone receptor-positive breast cancer to metastasize…”[iii]

To definitively determine that it was the disruption in the gut bacteria causing this phenomenon, the scientists transferred the abnormal gut bacteria to other mice via fecal transplant and sure enough, the receiving mice had the same issue:  aggressive metastasizing of tumor cells.

(By the way, for those of you familiar with breast cancers:  these findings only apply to hormone-positive breast cancer, not triple-negative.)

The authors of the paper point out that this study was not to look at whether or not the gut biome contributes to the initial development of breast cancer, but instead, to look at whether or not it affects the spread of the cancer cells, which ultimately will determine the long term prognosis.

Many chemotherapy drugs cause microbiome disruption and subsequent GI issues, raising several interesting questions.  Does this biome disruption ultimately put patients at risk for metastases?  And does this risk exist before the cancer diagnosis or is it the RESULT of the treatment for the cancer?  Trying to look at the bright side though:  if indeed microbiome alteration/depletion is a risk factor for the spread of breast cancer, then manipulating the microbiota should become a treatment option.  The next step for these researchers is to collect stool samples from women at high risk for metastatic breast cancer, and see if those with greater dysbiosis do indeed have a greater chance for the spread of the cancer.  (If they find some of the women do have high levels of dysbiosis, I sincerely hope they help them treat it!)

Obviously, there are the usual caveats to this research:  it’s early stage, it was done in mice, and so forth.  Whether or not it applies to humans remains to be seen.  However, I find myself concluding yet again, that it makes a hell of a lot of sense to take care of your biome now.  Can’t hurt, could help, as I always say.

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[i] https://www.cavalierdaily.com/article/2019/08/unhealthy-microbiome-found-to-be-linked-to-increased-spread-of-breast-cancer

[ii] Rosean, CB, et. al. Pre-existing commensal dysbiosis is a host-intrinsic regulator of tissue inflammation and tumor cell dissemination in hormone receptor-positive breast cancer. Cancer Research. 2019. DOI: 10.1158/0008-5472.CAN-18-3464

[iii] https://www.forbes.com/sites/victoriaforster/2019/06/11/disrupted-gut-microbiome-promotes-breast-cancer-spread-in-mice/#222a980d30de