Matthew J. Edlund M.D.

The Power of Rest

Huh? Gut Bugs Change Cancer Therapy?

It's not just about the drugs.

Posted Nov 19, 2016

It appears that a person's gut bug population influences the effectiveness of cancer therapy. A trial of immunotherapy on metastatic melanoma found those patients with a greater variety of GI bacteria did far better than those with more limited populations. Those with a lot of ruminococcus around were more likely to stay alive.

What Happened?

People with immunotherapy trials for melanoma at MD Anderson Cancer Center in Houston had their GI bacterial populations tracked into two groups—those who responded to treatment and those who did not, using standard case-control technique. The responders showed greater variety of bacteria than those who did not and rather different bacterial populations as well. In this case, diversity paid off.

What Was Cause, What Effect?

People with different gut bacteria have different diets and lifestyles. If you eat lots of vegetables, you not only have different kinds of bugs than if you choose meat with most meals, but you also get far more variety. Yet many other factors go into what bacteria populate your personal ecosystem, including where you travel, who you live with, and how much physical activity you enjoy, not to mention how much booze you imbibe.

Different bacterial populations change your propensity to certain illnesses; have shown major effects in autoimmune disease, stress, and depression susceptibility; and are used to treat illnesses like clostridium difficile, in which antibiotic use allows a generally unimportant bacterium to kill tens of thousands of people every year. Chances are your gut bug population will help determine what kinds of cancer and illness you’ll get. Because there is a potent effect of diet on the incidence of many types of tumor, it's no surprise to learn that your co-resident bacteria have this effect.

Why Should Bacteria Matter?

There are somewhere between 40 trillion and 100 trillion bacteria in your gut. Trying to keep this restive population at bay is one of the reasons your gut lining gets shed in a day. Depending on little understood circumstances, the immunological challenge these bugs represent also changes how the immune system operates. In terms of cancer therapy, they could
1. modulate overall immune responses,
2. change the absorption and penetration of drugs, and
3. shift the conformational form and metabolization of cancer drugs, among other effects.
Having a whole ecosystem inside you changes your immunity and response to cancer.

How Can This Best Be Understood?

You might start by viewing the body as a giant information system, with innumerable sets of living, interacting data. Living things are themselves not just carriers of information, but information itself. Importantly, gut bacteria don’t just make some of our vitamins, digest our foods, help us one day and fight us another. They dwell in fraught competition for space and territory with tens of thousands of other bacterial species and subspecies. Then come the other organisms living inside us, including bacteriophages—bacteria-hunting viruses—rickettsia, mycoplasma, fungi, and untold numbers of non-bacteriophage viruses.  It’s a really complicated world down there. Our political divisions look simple by comparison.  And the interactions among these different components is not much understood beyond knowing they're important to our health.

One way to put it all together is to look at the question of biological intelligence—how all living things accrue and apply knowledge, mostly unconsciously. We are usually not aware of how many cancers we form on any given day—it may be hundreds—or how our immune system causes many cancers to self-destruct, ingests others, and walls off still others. Most of the drama happens off stage—we notice only what goes on when cancer cells grow into multiple clones or do something very recognizable, like produce hormones that change our blood pressure or cause us to bleed.

Bottom Line:

Cancer kills one in three Americans. One of the most promising treatments now available is immunotherapy—helping to teach our own immune system how to kill the cancers it's failed to keep at bay. We've known for a long time such systems must work, as perhaps one in a thousand cancers will spontaneously remit.

Now it’s getting clear our own ecosystem—including our trillions of bacteria—has a role to play. Yet it's getting more probable that certain bacterial populations will make some treatments more effective. We may be able to induce those populations by lifestyle manipulations, like altering what we ingest and when. 

More interestingly, if bacterial and viral populations are part of cancer treatment, different patterns may prove helpful in preventing versus treating tumors. A diet brimming with fruit and vegetables may be a great idea in preventing colon cancer, but may not be the way to go once you've got it. 

Prevention and treatment are always contingent on just what kind of information system runs through us any given day. And that changes—every moment of every day day. Just another reason to put information approaches to the fore when preventing and curing disease—whether it’s cancer or colds.

So different immigrant and domestic bacteria will need our help—if they're to help us.