What Happens to Cancer Cells When You Exercise?

Added: 2026-05-22

[00:00:00]Aloha, I’m Irminne Van Dyken, MD, from  Out of the Doldrums. Welcome back.

[00:00:05]I want to start with a question  that sounds almost too bold.

[00:00:12]Can exercise help kill cancer cells? Now, before anyone runs away with that sentence, let me be very clear. Exercise is not chemotherapy.

[00:00:22]Exercise is not surgery. Exercise is not radiation.

[00:00:27]Exercise is not a magic shield against cancer. But there is a fascinating line of research suggesting that exercise may change  the internal environment of the body in ways that make life harder for cancer cells. And one of the most interesting mechanisms has to do with something very simple. Blood flow.

[00:00:51]When you exercise, your heart pumps harder.  Blood moves faster. Your arteries experience more force. Your muscles release chemical signals.  Immune cells move through the bloodstream.

[00:01:04]And if there are cancer cells  floating in that bloodstream, trying to survive long enough to spread somewhere  else, exercise may make that journey more hostile.

[00:01:19]That is the part I find so fascinating. Because most of us think about exercise in terms of calories, weight loss,  muscle tone, or heart health.

[00:01:30]But what if exercise also changes the  terrain that cancer cells have to survive in?

[00:01:36]What if movement does not just train  your body, but changes the battlefield?

[00:01:42]That is what we are talking about today. And one of the key ideas is something called shear stress. Shear stress sounds boring.

[00:01:52]It is not boring. It may be one of the most overlooked forces in the body. Shear stress is the mechanical force created when blood flows across the lining of  your blood vessels and across cells traveling through the bloodstream. In my nitric oxide video, I talked about shear stress because it is one  of the reasons exercise stimulates nitric oxide production. When blood flow increases across the  endothelium, that inner lining of the arteries, the vessels respond by making more nitric oxide,  which helps them relax and improve blood flow.

[00:02:28]That is the blood vessel side of the story. But here is the cancer side.

[00:02:32]A circulating tumor cell is not  sitting comfortably in a tumor anymore.

[00:02:36]It has broken away. It is floating.

[00:02:39]It is detached from its usual environment. It is exposed to immune cells, oxidative stress, collisions with blood cells, and  the physical force of moving blood.

[00:02:52]And during exercise, that force increases. So the question researchers asked was simple and almost shocking. Could exercise-level blood flow physically damage circulating cancer cells?

[00:03:05]In 2017, researchers published a study  in Scientific Reports called High Shear Stresses under Exercise Condition Destroy  Circulating Tumor Cells in a Microfluidic System.

[00:03:19]That title is not exactly winning any  poetry awards, but the idea is powerful.

[00:03:25]The researchers used a microfluidic system,  basically a lab model that can mimic blood flow conditions, and exposed cancer cells  to different levels of shear stress.

[00:03:37]They compared lower shear stress conditions with  higher shear stress conditions meant to resemble what might happen during vigorous exercise. And they found that high shear stress reduced the viability of circulating tumor cells. Let me say that in plain English.

[00:03:54]In this lab model, when cancer cells were  exposed to exercise-like mechanical forces, more of them were damaged or destroyed. Now, this is the part where we have to be honest.

[00:04:06]This was not a clinical  trial where people exercised and then researchers watched cancer disappear. This was a lab model.

[00:04:09]Cells in a device. Controlled conditions.

[00:04:11]So we cannot take that study and say, “HIIT kills cancer in humans.” That would be irresponsible.

[00:04:20]But the mechanism is intriguing. Because metastasis is not easy.

[00:04:25]For cancer to spread, a cell has to escape  the original tumor, enter the bloodstream or lymphatic system, survive circulation, avoid  immune detection, exit into a new tissue, and then successfully grow there. That is a brutal obstacle course.

[00:04:40]And exercise may make part of  that obstacle course even harder.

[00:04:44]I want you to picture this. A cancer cell breaks away from a tumor.

[00:04:49]It enters the bloodstream. But instead of floating through a slow, lazy river, it gets thrown into whitewater. Blood flow increases.

[00:04:57]Mechanical stress rises. Immune cells are moving.

[00:05:01]Muscles are releasing signaling molecules. The bloodstream becomes less comfortable for a cell trying to survive and spread. That image is powerful because it changes how we think about exercise. You are not just moving your legs.

[00:05:18]You are changing the physics of your bloodstream. Now, cancer cells are clever. Annoyingly clever.

[00:05:23]Some circulating tumor cells can adapt to  shear stress. Some can travel in clusters.

[00:05:29]Some can bind to platelets. Some can activate  survival pathways. Some can resist cell death.

[00:05:37]Cancer biology is never one clean, simple story. So the honest version is this: Shear stress may be one way exercise makes  the bloodstream more hostile to circulating tumor cells, but it is probably only  one piece of a much larger puzzle.

[00:05:57]And the larger puzzle is where the  story gets even more interesting.

[00:06:01]Because exercise does not only change blood flow. Exercise changes the chemistry of the blood.

[00:06:07]After you exercise, your bloodstream is different. That sounds dramatic, but it is true.

[00:06:09]Your muscles release myokines. Your immune cells mobilize.

[00:06:13]Your insulin sensitivity improves. Inflammatory signaling can shift.

[00:06:19]Stress hormones change. Growth factors change.

[00:06:22]Metabolism changes. And cancer cells are sensitive to their environment. They do not exist in isolation.

[00:06:29]They are constantly reading signals  from the tissue and blood around them.

[00:06:33]This is why I think one of the best ways to  explain exercise and cancer prevention is this: Exercise changes the internal terrain. That does not mean exercise gives you total control over cancer. It does not.

[00:06:47]But it does mean movement may  make the body less hospitable to cancer initiation, growth, or spread. Now let’s talk about another study that I found really interesting, especially  because of my work in breast surgery.

[00:07:02]A 2025 study in Breast Cancer Research and  Treatment looked at breast cancer survivors and compared a single bout of resistance training with  a single bout of high-intensity interval training.

[00:07:16]Researchers collected blood  before and after exercise.

[00:07:20]Then they exposed MDA-MB-231 breast  cancer cells to that serum in the lab.

[00:07:26]MDA-MB-231 cells are a commonly used  triple-negative breast cancer cell line, so they are often used in research  because they are aggressive and invasive.

[00:07:40]Here is what they found. After exercise, the blood serum contained higher levels of certain anti-cancer myokines. And when that post-exercise serum was applied to breast cancer cells in the lab,  cancer cell growth was reduced.

[00:08:00]The reduction was approximately  20 to 29 percent in vitro.

[00:08:04]That is not small. But again, we have to say it carefully.

[00:08:09]This does not mean one  workout treats breast cancer.

[00:08:11]This does not a mean exercise  replaces endocrine therapy, chemotherapy, immunotherapy, radiation, surgery,  or anything else your oncology team recommends.

[00:08:22]What it means is that even one bout of exercise  can change the blood environment in a way that affects cancer cells in a dish. That is fascinating.

[00:08:33]One workout. A measurable change in blood signaling.

[00:08:37]A measurable effect on  cancer cell growth in vitro.

[00:08:41]That should make us pay attention. Because the old way of thinking was: Exercise helps cancer patients feel better. Less fatigue.

[00:08:51]Better mood. Better strength.

[00:08:51]Better quality of life. All of that is true and very important.

[00:08:54]But the newer research is  asking a deeper question.

[00:08:58]Could exercise also affect cancer biology itself? Not as a cure.

[00:09:05]Not as a replacement for treatment. But as a biological signal that changes immune function, metabolism, inflammation,  myokines, blood flow, and possibly tumor behavior.

[00:09:18]That is a much more powerful conversation. Now let’s look at colon cancer.

[00:09:23]There was another study published in  the International Journal of Cancer that looked at what happened when serum collected  after a short bout of intense exercise was applied to colon cancer cells in the lab. The exercise bout was short, around 10 to 12 minutes of intense cycling. Not a marathon.

[00:09:39]Not an ultramarathon. Not some influencer doing burpees until their soul leaves their body. About 10 to 12 minutes of intense cycling.

[00:09:42]And the researchers found that post-exercise  serum changed the expression of more than 1,300 genes in colon cancer cells. Those genes were involved in processes like DNA repair, energy production,  inflammation, and cancer cell growth.

[00:10:01]That is wild. Ten to twelve minutes of intense exercise changed the blood environment enough that colon cancer  cells in a dish altered their gene expression.

[00:10:16]Again, that is a lab model. But it tells us something important.

[00:10:22]Exercise is not a vague wellness suggestion. Exercise creates rapid biochemical changes.

[00:10:28]The bloodstream after exercise is not the  same as the bloodstream before exercise.

[00:10:36]And cancer cells appear to respond  to that changed environment.

[00:10:42]That is one of the main messages  I want people to remember.

[00:10:45]Exercise changes the blood. Cancer cells are listening.

[00:10:50]Now let’s talk about the immune system. Because if we are talking about cancer prevention, immune surveillance matters. Your immune system is constantly scanning for abnormal cells. It does not catch everything,  clearly, but it plays a major role in recognizing and destroying cells that should not be there. Exercise can mobilize immune cells, including natural killer cells and cytotoxic T cells. Natural killer cells are especially interesting because they can attack abnormal or stressed  cells without needing the same specific priming that some other immune cells require. During and after exercise, these immune cells can move into the bloodstream in higher  numbers. They circulate. They patrol.

[00:11:37]So now imagine the exercise environment again. Blood flow is higher.

[00:11:41]Shear stress is higher. Muscles are releasing myokines.

[00:11:45]Immune cells are mobilized. Metabolism is shifting.

[00:11:49]Inflammation may be changing. This is not one mechanism.

[00:11:53]It is a coordinated physiologic event. That is why exercise is so powerful.

[00:11:59]It does not press one button. It pulls multiple levers at once.

[00:12:06]Now, let’s make this practical, because  otherwise this becomes a beautiful science story that nobody knows what to do with. What kind of exercise are we talking about?

[00:12:17]There are probably three major buckets. First: regular aerobic movement.

[00:12:22]Walking, hiking, cycling, swimming, jogging,  rowing, or dancing. Anything that gets your circulation moving and reduces sedentary time. And yes, dancing counts.

[00:12:34]Dancing can raise your heart rate, increase  blood flow, challenge coordination and balance, improve mood, and make movement feel less like  a chore and more like being alive in your body.

[00:12:47]That matters. Because the exercise you actually enjoy is the exercise you are more likely to repeat. This matters because consistent movement improves insulin sensitivity, blood pressure, blood  flow, inflammation, and metabolic health.

[00:13:02]And please do not underestimate walking. I know walking is not sexy.

[00:13:09]No one is making a superhero  movie called The Brisk Walker.

[00:13:11]But walking is one of the most accessible  anti-sedentary interventions we have.

[00:13:17]For many people, walking is the doorway. Second: strength training.

[00:13:19]This matters because muscle  is not just movement tissue.

[00:13:24]Muscle is metabolic tissue. Muscle is an endocrine organ.

[00:13:28]When muscle contracts, it releases myokines into  the bloodstream. These myokines can influence inflammation, immune function, metabolism,  and possibly cancer-related pathways.

[00:13:39]Strength training also improves insulin  sensitivity, functional reserve, body composition, and resilience. For cancer survivors, strength matters.

[00:13:49]For prevention, strength matters. For aging, strength really matters.

[00:13:55]Third: safe intensity. This is where the shear stress story becomes especially interesting. Vigorous exercise, intervals, uphill walking, cycling intervals, rowing intervals,  swimming intervals, dance intervals, or short bursts of harder effort may  create a stronger blood flow signal.

[00:14:15]That does not mean everyone needs extreme HIIT.

[00:14:19]For a fit person, intensity might  mean sprint intervals on a bike.

[00:14:23]For someone deconditioned, intensity  might mean walking faster for 30 seconds.

[00:14:27]For someone older, it might mean a hill. For someone who loves dance, it might mean one song where you really let  yourself move, followed by recovery.

[00:14:37]For someone in treatment or recovery, it  might mean supervised exercise tailored by their oncology or rehab team. Intensity is relative.

[00:14:47]The goal is not suffering. The goal is signal.

[00:14:51]That may be one of the most  important lines in this video.

[00:14:54]The goal is not suffering. The goal is signal.

[00:15:00]I think people need to hear that because cancer  prevention content can easily become moralistic.

[00:15:05]Eat perfectly. Exercise perfectly.

[00:15:08]Avoid everything. Optimize everything.

[00:15:10]That is exhausting. And honestly, it can become cruel, especially for people who already have cancer  and are wondering if they did something wrong.

[00:15:20]So let’s say this clearly. Cancer is complex.

[00:15:23]People who exercise can still get cancer. People who eat well can still get cancer.

[00:15:30]People who do “everything  right” can still get cancer.

[00:15:34]This is not about blame. This is about agency.

[00:15:39]There is a difference. Blame says, “You caused this.”

[00:15:45]Agency says, “There are still signals you can  send your body that may support resilience.”

[00:15:50]Exercise is one of those signals. Now, how strong is the evidence overall that physical activity reduces cancer risk? Large epidemiologic studies and major cancer prevention guidelines consistently associate  higher physical activity with lower risk of several cancers, especially colon cancer, breast  cancer, endometrial cancer, bladder cancer, kidney cancer, stomach cancer, and esophageal cancer. The exact numbers vary by study, cancer type, and activity level. But the overall pattern is consistent enough that physical activity is part of cancer prevention  recommendations from major organizations.

[00:16:31]For breast cancer specifically, physical  activity has been associated with lower risk, and among breast cancer survivors, exercise  is associated with better physical function, less fatigue, improved quality of life,  and in some studies, improved outcomes.

[00:16:48]But the reason I wanted to make  this video is because the mechanisms are becoming more interesting. This is no longer just, “Exercise because it is good for you.” That is true, but boring.

[00:17:00]The more interesting statement is: Exercise changes the internal environment that cancer cells have to live in. It changes blood flow.

[00:17:09]It changes immune surveillance. It changes myokines.

[00:17:12]It changes insulin and glucose handling. It changes inflammation.

[00:17:17]It may change the physical stress  on circulating tumor cells.

[00:17:22]That is a much more compelling reason to move. Now, let’s return to the original question.

[00:17:29]Can exercise help kill cancer cells? The careful answer is: In laboratory models, exercise-like shear  stress can damage circulating tumor cells.

[00:17:40]Post-exercise serum can suppress  cancer cell growth in vitro.

[00:17:46]Exercise can mobilize immune cells and release  myokines that may have anti-cancer effects.

[00:17:53]Human population studies show  that physical activity is associated with lower risk of several cancers. So yes, exercise may help create conditions that are less favorable for cancer cells. But no, we cannot say exercise alone kills cancer in the human body. We have to hold both ideas at the same time.

[00:18:16]The research is exciting. The interpretation needs restraint.

[00:18:22]That is how we stay credible. Now, let’s give people a simple framework.

[00:18:27]If you want to use exercise as part of a  cancer-prevention lifestyle, think about this: Move most days. Build muscle two or three days per week.

[00:18:36]Include safe bursts of intensity if appropriate. Break up long sitting time.

[00:18:43]Recover well. Sleep.

[00:18:46]Do your recommended cancer screenings. And if you are currently in cancer treatment or recovering from treatment, work with your oncology  team before changing your exercise routine.

[00:18:59]Because the point is not to crush yourself. The point is to create repeated, healthy signals.

[00:19:05]A walk is a signal. A strength session is a signal.

[00:19:10]A hill is a signal. A bike interval is a signal.

[00:19:14]A dance class is a signal. Your body is listening.

[00:19:18]And perhaps, in some very real biological  ways, cancer cells are listening too.

[00:19:23]So the next time you exercise, I want  you to picture something different.

[00:19:26]Not calories. Not punishment.

[00:19:32]Not earning your food. Picture your bloodstream changing.

[00:19:36]Your heart rate rises. Blood flow increases.

[00:19:40]Your vessels feel that force. Your muscles release chemical messengers.

[00:19:46]Your immune cells mobilize. Your metabolism shifts.

[00:19:51]You are changing the environment that  every cell in your body lives in.

[00:19:56]That is the power of exercise. Not because it is trendy.

[00:20:00]Not because it looks good on a smartwatch. But because movement is one of the oldest biological signals we have. Move.

[00:20:09]Adapt. Repair.

[00:20:10]Defend. Stay resilient.

[00:20:11]If you found this helpful, I would  love to hear from you in the comments.

[00:20:15]Have you ever thought about exercise  this way, not just as fitness, but as a way of changing the  internal terrain of the body?

[00:20:25]And if you are interested in this topic, I  also have videos on nitric oxide, blood flow, the oral microbiome, and how exercise  trains your blood vessels from the inside.

[00:20:37]As always, this is for education and not  personal medical advice. If you have cancer, are in treatment, have heart disease, chest  pain, arrhythmias, uncontrolled blood pressure, or are new to exercise, please talk  with your own clinician or oncology team before starting a new exercise program. Cherish your health always, and aloha.