Gut Microbiome & Cancer: How Gut Health Affects Treatment & Prevention

Brad Power and Kayla Yup January 22, 2025 “Hopefully I gave you a little bit of Gestalt on what's coming and how your microbes can interact with your immune system and how you can manipulate it with your diet and things like that that are coming. It's always a sensitive topic in that you have to be careful, especially with patients that are in the cancer journey, because it's a vulnerable time and you're looking for stuff.

I want to make sure that I'm an advocate for you when you're looking at the microbiome and making sure we're not overselling something.

, gene mutations, such as BRCA1 and BRCA2); environmental factors (exposure to harmful substances in the environment, such as chemicals in tobacco smoke, ultraviolet rays from the sun, and asbestos); infections; lifestyle factors (being overweight or obese, not having a healthy diet, not getting enough physical activity, or drinking alcohol); hormones; and stress or a poor mental health state.

Beyond the prevention of cancer, patients also have challenges with managing cancer symptoms, such as pain, depression and anxiety, fatigue and weakness, loss of appetite, weight changes, nausea and vomiting, constipation. Both the prevention of cancer and the management of cancer symptoms can be influenced by your gut microbiome. Your microbiome regulates cancer initiation, progression, and responses to therapy.

An altered microbiome has been tied to specific types of cancer and to the effectiveness of cancer treatments, suggesting that the profile of your microbiome could be a biomarker for your cancer diagnosis or prognosis. According to research from the American Cancer Society, approximately 40% of cancer cases in the United States are linked to modifiable lifestyle factors, meaning they could potentially be prevented through lifestyle changes.

Lifestyle choices, particularly diet and exercise, significantly impact the microbiome, which in turn can influence your development and progression of cancer. Michael Liss, MD, PhD, is uniquely qualified to lead a discussion about the role of the microbiome in cancer, especially prostate cancer.

He is a urologic oncologist (a doctor who specializes in diagnosing and treating cancers of the urinary tract and male reproductive organs), and has a PhD in translational science, with a focus on natural products and the microbiome. He has a masters degree in clinical trials and is a professor at UCSD. What is the microbiome? The microbiome is the collection of microorganisms that live on or inside a person, animal, or plant.

These microorganisms include bacteria, viruses, and fungi. The microbiome is dynamic and changes over time in response to environmental factors like diet, exercise, and medication. How can the microbiome influence your development of cancer (for good or bad)?

The microbiome, particularly the gut microbiome, can significantly influence cancer development by either promoting tumor growth through inflammation and harmful metabolites produced by certain bacteria, or by suppressing tumor development through immune regulation and anti- tumorigenic metabolites produced by beneficial bacteria, essentially acting as a double-edged sword depending on the microbial composition and balance present; a disrupted microbiome is often linked to increased cancer risk.

Brad Power This is the Cancer Patient Lab. We're honored today to have Michael Liss with us. Dr. Liss is at UC San Diego. He was referred to us by Cancer Patient Lab co-founder Brian McCloskey. He's going to be talking about the gut microbiome and how it impacts cancer, prostate cancer, specifically, but in general, for other cancers and what's at the cutting edge of the connection with the microbiome. This is for information purposes only.

This is not medical advice. We try to arm patients with information that they can take to their medical team. We are a patient-led, all volunteer nonprofit, and we welcome donations, which you can do through our website and the donate button. Michael Liss 1:16 I'll talk about the gut microbiome. You've probably heard a lot about this in the comings and goings and in the news.

I'm a professor at UCSD, and I'm the director of clinical trials for the center of microbiome innovation. I have a company focused on this particular topic, but I won't go into the very specifics until the end, when I'll make a couple comments about it. This is the agenda. [We’ll talk about] the microbiome, a little bit about prostate cancer algorithms, and how we may be able to use this information. And then we'll get into the questions.

This is how we think about microbes. This is a museum, actually, in Amsterdam. Of course, somebody like me would go to something like this. That's why it exists. ” It takes us all the way back to the 1800s when we start looking at bacteria. We had them out on these little plates. You had to have very specific plates to grow certain bacteria, and so we were a little bit limited. ’ Well, most of it's in the gut.

That's where a lot of the action happens. So a lot of these bacteria are there. And they're not all bad. I usually show this slide because these particular birds clean the teeth of alligators, and they're not going to eat this bird, because it's basically its toothbrush, and it prevents disease and things like that. So we think something is maybe horrible when we see these names, right, but it actually may be beneficial.

And I think that's where the microbiome (the community of microorganisms that exist in a particular environment) and all these microbes with fancy names get a little bit confusing when we start talking about them. Not all of them are bad. When we say biome, we have to go back to fourth grade biology.

If you live in the Mississippi River Valley, you're going to have different bacteria or plants and things like that than you would if you're living on the mountain coast. This concept goes throughout our body, like what is in our colon is not the same as our skin, and we could use those differences now and we can start comparing diseases.

Even within the Sierra Nevada Mountains, if I put in or take out a wolf, well, that changes the whole ecosystem. That's how we start thinking about the microbiome, is that it's not just one bacteria, they're all communicating. ’ When you see some of the [research] papers come out, this is how we compare different things. If we have samples from different patients, and we want to compare them.

Well, we take sample A, we count three greens, two purples and two browns. Okay, that's that. And we kind of set up a whole table like this, and now we set it on three different axes to see, okay, where, in three dimensions, does this person lie? And we can see that B and D are more closely related than B and A. And so that's how we can do these, some of these comparisons of different microbes. This is the Human Microbiome Project.

So this came out quite a while ago, using 4000 samples, and that's how we grouped different organ sites, essentially. When we talk about the microbiome, there are different sites, right? So if we're talking about prostate cancer, at the very bottom of this slide, the very degenerative urinary microbiome that we can get from directly in the tissue or in the urine is very different from what we're talking about in the gut.

So the gut can be manipulated by diet and things like that, whereas the urinary stuff may be manipulated in a different way. When we moved to prostate cancer, we knew it's a very common disease, and when I first started thinking about this, I had a lot of microbiology background, and I was looking for a way to kind of marry these things, because I felt like they were related.

And I started looking at inflammatory bowel disease, and there were some papers that had come out saying that there's this link between gut inflammation and prostate cancer. ’ They're not connected. They're close to each other, but there's no connection between the colon and the prostate. And so this inflammatory aspect piqued my attention. And then basically, we said, okay, there's a healthy microbiome and a cancerous microbiome.

Can this start impacting what we're looking at? This is a diagram showing the colon, the prostate, and the bladder, and how we void out the urethra. There's different concepts of things going on here. So within the prostate, there can be various organisms. [Some questions about the microbiome here are] can they cause DNA damage? Can they make certain substances that are within the prostate?

Or is it a chicken or the egg situation where a cancer can form and then maybe the microbes that can live in that environment are different than if there wasn't a cancer there. So can we use that as a biosensor? The other aspect in the gut is, as we get older, men can have urinary tract infections or inflammation or something like that, and those bacteria usually communicate from the rectum over to the urethral urinary system.

And so things that are in the colon can directly impact the prostate, but they also can make microbes and cause generic inflammation and things like that that we want to watch for. We first published on this topic back in 2017. I basically used patients that had cancer versus not, and I used their gut microbiome, and we showed that there were some differences.

And if you kind of make a line diagonally through this, you can see a lot more orange on one side and more blue on the left side. ) and we came up with B vitamins, which are folate and biotin. Now, [folate] is not something that you take.