May 12, 2017
4 min read

Exercise has ‘astounding’ effect on breast cancer recurrence, mortality

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Exercise appeared far more likely than other lifestyle factors to reduce the risk for breast cancer recurrence and mortality, according to a review published in Canadian Medical Association Journal.

Although physical activity showed the strongest benefit, people who did not gain weight also demonstrated lower risk for breast cancer recurrence and mortality.

Ellen Warner

Ellen Warner, MD, FRCPC, FACP, affiliate scientist of Sunnybrook Health Sciences Center in Toronto, and colleagues reviewed 67 published studies to determine which lifestyle factors most influenced prognosis and overall health among women with breast cancer.

Exercise reduced breast cancer recurrence and mortality by 40%, whereas weight gain of more than 10% after diagnosis appeared associated with increased mortality risk.

When researchers assessed the effects of diet on prognosis and overall health, they determined soy consumption may not be as harmful as previously suggested for women diagnosed with breast cancer. In fact, soy consumption actually may reduce recurrence risk, results showed.

HemOnc Today spoke with Warner about the study, the importance of the results, and what health care providers should tell patients regarding the importance of regular physical activity.

Question: What prompted this research?

Answer: I have been a medical oncologist for many years, and many patients with breast cancer want to do something beyond conventional therapy. In some cases, it is extreme. They go the naturopath and may get a dozen or more types of alternative therapies. Many start strange diets based on information they get from the internet, family or friends. They go off sugar, meat, dairy, soy and so on. They believe they are helping themselves, but they really are on a restrictive diet. However, I have always promoted a healthy lifestyle for these patients. Some data suggest this may reduce risk for recurrence, and reams of data — both published and my own empirical observations — show exercise and keeping weight gain down have physical and psychological benefits. A former student of mine approached me about supervising her on a project. I knew her background was in nutrition, and she was an athlete, so it seemed like the perfect fit to conduct this study with her.

Q: What did you find?

A: Two things really do help in a statistically meaningful way. The first is exercise — not intense exercise, but moderate exercise people can be incorporated into their everyday life, such as brisk walking, dancing or cycling. Thirty minutes of exercise five times per week is all one needs to achieve a 40% reduction in breast cancer recurrence and death. This is just astounding. The other very helpful thing is to not gain weight. Weight gain increases recurrence risk; conversely, not gaining weight reduces recurrence risk.


Q: What did the data suggest concerning soy consumption?

A: All of the evidence we have on soy — as related to humanly consumable amounts — shows that, if anything, it may be protective and lower risk for recurrence. Soy is a wonderful alternative to high-fat and meat products. One of the biggest myths is that soy is harmful; the phytoestrogens that are talked about actually are weak estrogens and are not bad. The lowest rate of breast cancer in the world at one point was in Japan. This was reported when people there still ate the traditional diet, which included a very high soy intake compared with the typical Western diet.

Q: Did any of the findings surprise you?

A: I was surprised about how big the effect was for exercise — 40% is pretty impressive. We mostly see a small 10% to 20% effect of lifestyle factors on diseases.

Q: What implications do the se d ata have for clinical practice?

A: These data give all clinicians more ammunition to reinforce the importance of exercise and not gaining weight.

Q: What are some other potential benefits of regular physical activity?

A: Many patients become depressed and anxious, particularly if they had an anxiety disorder or depression before their diagnosis. A breast cancer diagnosis can significantly worsen these conditions. Exercise is one of the best ways to improve mood and decrease anxiety. Also, data suggest exercise can reduce side effects caused by many treatments.

Q: What should future research entail?

A: We have many unanswered questions. We suspect that diet may be important, but we are not certain as to exactly what components are important. We need more prospective trials in which people are randomly assigned to an intervention or a control arm. The problem is that with diet research, it is very hard to tease out individual dietary factors. In addition, the same people often exercise, watch their weight, eat healthier, and abstain from drinking or smoking. Trying to tease out each individual factor is tough. Randomly assigning people to a higher soy diet or lower soy diet, for example, is a much stronger scientific way to study these things.

Q: Is there anything else you would like to mention?

A: There are two key things I want to emphasize. First, all patients in our study received conventional treatment. Patients should not think they can skip chemotherapy and assume that exercise alone will decrease their risk for recurrence by 40%. We only know that exercise works in people who have received standard treatment. Second, some patients are going to recur regardless of how many positive lifestyle changes they make, and they should not feel guilty if this happens. It is not because they did not go to the gym in the previous month or because they put on 5 pounds over the holiday. Most of these cancers have their own biology and will recur — or not recur — despite lifestyle changes. – by Jennifer Southall


Hamer J, et al. CMAJ. 2017;doi:10.1503/cmaj.160464.

For more information:

Ellen Warner, MD, FRCPC, FACP, can be reached at Sunnybrook Health Sciences Centre, 2075 Bayview Ave., Room T2 053, Toronto, ON M4N 3M5; email:

Disclosure: Warner reports no relevant financial disclosures.