Probiotics for Breast Cancer? (or…Talking About Needing More Research…)

I was surprised, but not surprised, by an article I read last night on the potential use of probiotics in treating breast cancer (BC).[i]  As several friends have already battled BC, this is a topic of particular interest to me.  I knew there was a known inflammatory component to some forms, and a microbiome connection, and have actually written before about this  on this blog.

First, some statistics, for those of you who don’t know just how prevalent BC is:  breast cancer “…is the most frequent cancer in women, the second most common cancer worldwide, and the second primary cause of cancer-related deaths.”  So yes, I think research into anything that might help is more than merited!

A bit of education, in case you are unfamiliar with breast cancer:  the most common kind is hormone (estrogen and/or progesterone) receptor positive. Excess estrogen is a known risk factor for the development of BC:  “The increase in the amount of free estrogens for reabsorption contributes to the risk of development of hormone-driven malignancies such as BC.”  Gut bacteria play a major role in modulating this reabsorption and the circulation of estrogens.

As I mentioned in my last post on this subject, antibiotics and dysbiosis appear to be a major risk factor for the development of BC, and indeed, factors which affect the gut bacteria, such as diet, also affect BC development.  For example, “Strict vegetarians have increased fecal excretion of conjugated estrogens compared with non-vegetarians, leading to decreased plasma estrogen concentrations and protect against subsequent BC risk.”  High cholesterol levels are another known risk for the development of BC, so this may be the connection.  A vegan diet is typically much higher in fiber than other diets, and certainly affects the composition of the gut flora.  Alcohol consumption, which is another established risk factor, also alters gut bacterial composition in animal models and, at the very least, in humans who abuse alcohol (and/or have alcohol cirrhosis of the liver).   In humans, “…alcohol intake after BC diagnosis is associated with both increased risk of recurrence and deaths. There doesn’t seem to be a lot of research on the microbiome and occasional use of alcohol.

Basically all studies on the potential benefits of probiotics to treat this awful disease have been done in animals, and the results have been really very promising.  Here are 2 examples:

  1. Lactobacillus acidophilus was given to rodents starting 2 weeks before they had BC tumors transplanted into them, and the probiotic was continued for 30 days afterwards.  “The results showed a significant increase in the survival time among the L. acidophilus group compared to that of the controls, demonstrating that this treatment can promote the immune responses…Additional animal studies confirmed that oral administration of acidophilus displays anticancer activity to mice bearing breast tumors.”
  2. Another, particularly virulent form of breast cancer – not associated with hormones – is called triple negative. Mice with triple negative tumors were fed kefir, which led to greatly reduced tumor size.
  3. Other studies which have shown positive effect were done with Lactobacillus casei, yogurt and Lactobacillus plantarium.

Thus far, there has been very little clinical work done with humans.  One Japanese study asked 306 women with BC, and 662 women without, about their diets, lifestyles and other risk factors and found that regular and long-term consumption of L. casei Shirota (found in Yakult yogurt, and which I have written about before – for example,  here ) was “…significantly associated with decreased BC risk in Japanese women.”

The conclusion of the article:  the results of what in vivo and in vitro studies that we have is that, “…probiotics may have an anticancer systemic property, enhancing the systemic immune system, useful for interventions to prevent and control progression of BC.”  Sounds like it might be yet another, “can’t hurt and could help, so why not do it” scenario.


[i] Mendoza, L. Potential effect of probiotics in the treatment of breast cancer.  Oncology Review. 2019;13(422).  doi: 10.4081/oncol.2019.422

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