Exercise helps. This is almost universally true. Whatever the ailment, if you get moving, you’ll do better. According to recent studies, this is true for cancer as well. Exercise is associated with a substantial decrease in cancer incidence as well as with a better response to chemotherapy or radiotherapy. This is so uncontroversial by now that first studies are looking at exercise during chemotherapy, by letting the patient pedal while the drugs flow.
I’m lying in a bed rather lifelessly, moving nothing more than my fingers to compose this entry. I look out of the window at trees that are transitioning from colorful to stripped of all leaves. How much should I exercise? What is going on inside me when I exercise? To address some of these questions, a friend had sent me a review that digs a bit deeper into the molecular processes underlying the body’s response to cancer and how exercise can strengthen it.
The immune system is well equipped to battle cancer. It sends a variety of leukocytes, such as natural killer cells that can kill tumor cells directly and T and B cells as part of the adaptive immune response. The main problem is that the tumor environment is modified from the normal cellular environment to make it harder or even impossible for immune cells to infiltrate tumors. Tumors are low on oxygen and glucose and high on lactate, and generally in an acidic microenvironment. This is all caused by their uninhibited growth. A corollary is a resistance to the body’s immune response.
Regular exercise modifies the cancer environment to bring it closer to the normal state. Curiously, a solid blood supply is important for this. I always thought one wants to cut the tumor off from the blood supply to deprive it of nutrients, but it seems more important to open a passage for leukocyte to enter cancer cells. Exercise helps with this. At the same time, one of the ingredients of my chemo cocktail is avastin, a drug that inhibits blood vessel formation. Unless I misunderstand something, this makes no sense at all.
The review continues to outline how exercise helps the immune system. Not all exercise, though. Moderation is good. Heavy, long exercise can even suppress the immune system (if maybe only temporarily). Nothing in science is easy or straightforward. Plenty of graduate students have abandoned their PhDs because they couldn’t get over the contradictions.
After reading the review, I know a bit more about the immune system and its interaction with cancer cells (though the topic remains mighty confusing), but what’s the practical benefit? In particular since the review warns that “there are no studies that directly link exercise-induced changes in the tumor physiologic microenvironment with changes in tumor immune response.”
Is the effort for nothing then? This is hard to believe. Absence of evidence is not the same as evidence of absence. From the scientific facts outlined in the review, it seems eminently sensible to continue with the exercise program, always ensuring that I keep my effort controlled and my heart rate below the aerobic threshold. With the kit I’ve assembled over the last few weeks, this is easily possible. The only problem is my motivation, but if a possibly increased chance of survival doesn’t motivate me, what will?
For comfort and because it confirms what I think is right, I take one sentence from the review and run with it. “Chronic treadmill training increased tumor cell cytolysis by peritoneal macrophages by 50%.” This is where I want the action to happen. Clearing the peritoneum of cancer cells is the most difficult task. If exercise helps with this by even a bit only, it’s worth doing it.
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