A study from the Karolinska Institutet in Sweden shows that repeated bouts of exercise slow the growth of, and help to prevent recurrences of, cancers (eLife, Oct 23, 2020;9). The authors showed, in both mice and humans, that exercising muscles release into the bloodstream chemicals that increase production of CD8+ cells that an individual’s own immune system uses to kill cancer cells. The authors also showed that they could transfer CD8+ cells from exercising mice with cancer to reduce cancers in mice who did not exercise.

Exercise is now recommended as part of the treatment for cancer by the American College of Sports Medicine, the American Society of Clinical Oncology, the National Comprehensive Cancer Network, the American Cancer Society, the Oncology Nursing Society, the Commission on Cancer and the Cancer Foundation for Life, because studies show that exercise can help both prevent and treat cancer (Med Sci Sports Exer, November 2019;51(11):2375-2390).

How Exercise Affects Cancer
Your body makes millions of cancer cells every day. A healthy immune system recognizes that the cancer cells are different from normal cells, so it destroys the cancer cells. Cancer develops and spreads only when your immune system fails to recognize and control cancer cells. Today, many cancers are being treated with special drugs that try to help your immune system recognize the cancer cells and then seek them out and destroy them (as a healthy immune system would normally do). This recent research from Sweden is based on the knowledge that your immune system kills cancer cells primarily by sensitizing cytotoxic T cells so they recognize the difference between normal cells and cancer cells, and then try to attach to and kill the cancer cell. The authors of this study showed that just minutes after a person exercises intensely on a bicycle, their exercising muscles release certain chemicals that stimulate the immune system to activate the CD8+T cells that recognize and kill cancer cells and do not attack normal cells. The authors hope that their research will lead to the development of new ways to immunize people against cancer.

Regular Exercise is Associated with Reduced Risk for Cancer
• Compared to sedentary people, regular exercisers have a 69 percent reduced risk of being diagnosed with 22 different cancers including those of the colon, breast, endometrium, kidney, bladder, esophagus, stomach, lung, breast, prostate, myeloma, head and neck, pancreas, ovary, and prostate (CA: A Cancer Journal for Clinicians, October 16, 2019).
• A prospective study of 1.44 million people, ages 19 to 98, in the U.S. and Europe, followed for 11 years, found that a regular exercise program was associated with a lower risk of cancers of the colon, breast, endometrium, esophagus, adenocarcinoma, liver, stomach, kidney, head, neck, rectum, bladder and lung, and myeloid leukemia and myeloma (JAMA Internal Medicine, May 16, 2016).

Exercise Helps to Treat Cancers
An extensive review of research shows that exercise:
• reduces the side effects of chemotherapy treatments including nausea, fatigue, anxiety and depression, and increases bone strength and muscle mass (Curr Treat Options Oncol, 2008;9:135-46)
• increases the percentage of people who are able to complete full-dose chemotherapy regimens (J Clin Oncol, 2007;25:4396-404)
• can increase tumor sensitivity to chemotherapy (Cancer Prev Res (Phila), 2013;6:925-37)
• reduces heart damage from chemotherapy (Circulation, 2011;124:642-50)
• markedly reduces arm swelling from extensive breast cancer surgery (N Engl J Med, 2009;361:664-73)
• is associated with a 50 percent increased survival rate in patients treated for breast cancer (JAMA, 2005;393:2479-86) and colon cancer (J Clin Oncol, 2006;24:3535-41)
• is associated with a 70 percent risk reduction of high-grade, advanced or fatal prostate cancers (Arch Intern Med, 2005;165:1005-10)

A regular exercise program reduced carcinogenic inflammation, strengthened the immune system and improved mental processing by increasing apoptosis and by lowering cancer-inducing insulin-like growth factor 1, DNA damage and gene mutations (Br J Cancer, 2011;105:S52-73). Exercise reduced cancer patients’ anxiety, depression and fatigue, and exercise specifically can reduce the massive upper arm swelling and fluid retention common in women treated for breast cancer (Med Sci Sports Exerc, Nov 2019). Exercise also helped to prevent cancer patients’ inactivity that increases risk for heart failure (Med Sci Sports Exerc, 2010;42:1409-1426).

Rules for Exercise for Cancer Patients
Cancer patients should check with their doctors prior to starting a new exercise program. If possible, most people with cancer should try to exercise at least three times per week, at a moderate intensity such as brisk walking, for at least 30 minutes, and if possible, they should also try to lift weights twice a week. I can recommend no specific exercise program for cancer patients because the amount of exercise a cancer patient can do is limited by level of fitness, extent of disease, treatment regimen and other variables. In general, all exercisers – healthy or not – should follow these rules:

• Stop exercising when your muscles start to hurt, burn or feel tight. If you keep on exercising, your muscle fibers can start to tear and run out of their stored sugar supply. Your body always talks to you and tells when this is happening. Failure to listen to your body is the most common cause of exercise injuries.

• Take the day off when your muscles feel tight or hurt after you have warmed up for five minutes or more. It is normal for muscles to feel sore when you first get up in the morning, but they should feel better after you have exercised for five to 10 minutes. Soreness after warming up means that your muscle fibers are damaged and are at increased risk for tearing if you exercise that day. Sometimes you can get away with exercising at reduced intensity on days when your muscles feel sore, but often it is best to just stop for the day.

• Stop exercising immediately if you feel increasing soreness in one spot, which can mean that a muscle is about to tear or go into a spasm. You can prevent many injuries just by stopping exercising when you feel pain in one spot and do not have pain in the same spot on the other side of your body.
Fitness for Cancer Patients and Survivors
Cancer Treatment Should Include Lifestyle Improvements

Caution: Exercise can cause heart attacks in people who already have blocked arteries, particularly if you have any markers for arteriosclerosis: high blood pressure, cholesterol or blood sugar, or a lot of belly fat (more than two inches when you pinch the skin over your belly). Check with your doctor.