Your microbiome and cancer

Lab studies indicate that the composition of your microbiome can help fight cancer. Your microbiome is the unique set of bacteria you carry around with you, or it might be more accurately said that they carry you around since they outnumber body cells ten to one.

Checkpoint inhibitors prevent T-cells from recognizing cancer as friend.

Checkpoint inhibitors prevent T-cells from recognizing cancer as friend.

Your microbiome can affect immune response, which in turn can fight cancer. Unfortunately, your immune system doesn’t always recognize cancer as a threat. Solid tumors are especially hard to target. Skin and lung cancers form solid masses that are hard to penetrate compared to liquid tumors in the blood.

Cancer cells hide by fooling immune cells into thinking they are not foreign at all. To determine friend or foe, immune cells check for a protein. If they find it on cancer cells, they appear as friends.

One innovative cancer treatment involves an immunotherapy drug called checkpoint inhibitors which do just what the name suggests –they block the checkpoint that looks for friend or foe. Seeing no friend because they are blocked, immune cells mount a defense.

This is where the microbiome comes in. Gut bacteria affect our immune system’s inflammatory response. Scientists at the University of Chicago found that mice responded to cancer invasion in varying degrees according to the type of bacteria in their guts (Scientific American, April, 2016).

Mice that were fed a particular strain of bacteria were able to fight skin cancer better than those who weren’t. When poop from the cancer-fighters was transferred to others, tumor growth slowed.

Remarkably, when checkpoint inhibitors were given to both the mice with the particular bacteria and those with the fecal transplant, tumors disappeared completely in the former and was reduced in the other. Then, when the mice with the fecal transplant were also given the bacteria, they were cured completely.

French scientists had similar results in which both the checkpoint inhibitor and a different bacteria were given. Next, the scientists gave antibiotics to the mice which killed bacteria, including the beneficial ones. The conclusion is obvious: doctors need to be cautious in prescribing antibiotics to cancer patients.

Not any bacteria will do. The Chicago team used either Bifidobacterium longum or Bifidobacterium breve. The French used Bacteroides. Yogurt contains Bifidobacterium lactis or Bifidobacterium bifidum remains untested.

Fine-tuning the immune system is a tricky business. The wrong kind of bacteria could cause the immune system to become too active and attack normal tissue. Autoimmune diseases include type-1 diabetes, inflammatory bowel disease, psoriasis, and rheumatoid arthritis. The effect of general bacteria on fine-tuning the immune system still needs to be investigated.

“Obviously we need to categorize the bacteria in the human microbiome and their potential antitumor effects more completely before we can recommend any treatments in people,” cautions the Chicago team.

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