Exercise: A Healthy Way To Help Prevent Cancer's Return?

Issue 24 Winter/Spring 2015

Picture of cancer patient exercising

Regular exercise, along with recommendations for other lifestyle behaviors, such as maintaining a healthy diet and weight and avoiding smoking, has become established as a cornerstone therapy for the prevention of numerous different chronic diseases, such as heart disease, stroke, diabetes, and even neurodegenerative conditions.

Similarly, among individuals who are diagnosed with these disorders, exercise-based rehabilitation is often the 'firstline' therapy for treatment, as well as secondary prevention of these conditions.

In the area of cancer, there is now also convincing evidence that individuals who report participation in regular exercise according to the national guidelines – at least 150 minutes of moderate- intensity exercise, or 75 minutes of vigorous exercise per week – have a 30% to 50% reduction in their risk of colon cancer and breast cancer, as well as a 10% to 30% reduction in their risk of other common cancers, such as prostate and lung cancer.1

Despite this evidence and in stark contrast to its established role in other non-cancer chronic diseases, exercise-based rehabilitation for people diagnosed with cancer had, until recently, received minimal attention.2 However, the good news is that over the past two decades, research interest in the potential role of regular exercise in individuals with cancer has started to emerge. These studies have examine whether participating in regular exercise is safe and can be tolerated by people who have completed cancer therapy or even those undergoing cancer therapy, as well as whether exercise can help patients cope and recover from their cancer experience.

Promisingly, findings from approximately 90 studies indicate that participating in regular exercise is safe and well-tolerated by patients with many different types of cancer (even in those undergoing cancer treatment) and also offsets many of the acute as well as persistent side-effects of cancer treatments.2

While 90 studies may seem like a large number, this is actually relatively small in comparison to the number of studies that have investigated the effects and role of exercise in heart disease or type II diabetes. However, interest in this field, which has now adopted the name 'Exercise-Oncology', is continuing to grow at a rapid pace, with numerous studies currently underway that are answering the next generation of questions in this field.

Questions that are critical to address include: (1) what is the optimal amount (or dose) and type of exercise to offset, and recover from, the adverse effects of cancer and cancer treatments, (2) is exercise equally effective across the many different types of cancer and cancer treatments, (3) how does exercise improve or off-set the side-effects of cancer treatments (in other words, what are the mechanisms of action), and (4) when should cancer patients exercise – immediately at diagnosis, during treatment, or should patients wait until after all treatments have finished.2 The answers to these questions will be critical to informache design and standardization of standard exercise prescription and exercise rehabilitation guidelines for cancer patients and survivors.

Picture of elderly male exercising

Another question that is starting to receive considerable interest in the field of exercise-oncology research and clinical practice is whether the benefits of exercise extend beyond helping patients cope with, as well as recover from, the side effects of cancer and cancer treatments to impacting the development and progression of cancer itself.

Several observational studies have investigated the relationship between the amount of exercise individuals with cancer are engaging in (typically following the completion of cancer therapy) and the risk of cancer recurrence, as well as dying from cancer. Remarkably, findings from these studies suggest, in general, that cancer patients engaging in a level of exercise that is consistent with the national guidelines have between a 10% to 50% reduction in the risk of cancer recurrence as well as dying from cancer.3,4

The majority of these studies have been performed in women with early-stage breast cancer but there is also evidence for this association in patients with colorectal, prostate, and ovarian cancer.

While promising, it is important to note that these studies have important limitations. First, these studies ask patients to self-report how much exercise they are participating in, which may lead to inaccuracies in the manner in which exercise is reported and is subject to bias. Second, these data do not prove cause and effect. In other words, while these studies looked at the association between exercise levels and recurrence, they did not randomly allocate patients to an exercise training group (wherein the amount and volume of exercise could be tightly prescribed and monitored) versus a non-exercise control group. This type of study is required to 'prove' that exercise leads to a decreased risk of recurrence. Several large studies are currently underway to investigate this very question.2 Those studies will take several years to complete, but the first results should be available within the next few years.

An important related question is, if exercise does lower the risk of cancer recurrence, how exactly is this happening? We have a firm understanding of how different standard cancer treatments, such as radiation and chemotherapy, inhibit cancer cell growth and spread, but currently have very little insight into how exercise may influence these factors. In comparison to the different types of conventional cancer treatments, exercise may seem like a very simple therapy.

However, the body's response to exercise is extremely complex and surprisingly not very well understood. We are beginning to understand that exercise can profoundly alter a wide variety of factors that are circulating in the blood stream, such as levels of factors related to metabolism, immune function, sex hormones (such as estrogen or testosterone), and inflammation. Interestingly, a number of these same factors are also implicated in the initiation and progression of cancer. A critical goal of ongoing efforts is to understand how different levels (doses) of exercise alter these circulating factors and then, secondarily, how change in these factors alters the behavior and biology of cancer cells.3

In summary, there is growing recognition of the beneficial role of regular exercise following a cancer diagnosis to offset the adverse side effects of cancer and its treatments. Emerging data are also suggesting a previously unexpected role of exercise – as a novel approach to potentially reduce the risk of cancer recurrence. However, it is important to stress that the current evidence base is small and many more tightly controlled studies are required to rigorously test this question. In the interim, all individuals with cancer should be encouraged to avoid inactivity (being sedentary) and attempt to achieve the national exercise guidelines on a weekly basis.

In general, such guidelines can be achieved by slowly increasing the number of times exercise is performed each week (progressing from 2 to 5 days/week over a 3 to 4 week period) as well as increasing the duration of each exercise session (from 15 to 45 minutes/session) over the same time period.

Lee W. Jones, PhD

Lee W. Jones, PhD
Memorial Sloan Kettering Cancer Center
New York, NY

References

  1. Friedenreich CM, Orenstein MR: Physical activity and cancer prevention: etiologic evidence and biological mechanisms. J Nutr 132:3456S-3464S, 2002
  2. Jones LW, Alfano CM: Exercise-oncology research: past, present, and future. Acta Oncol 52:195-215, 2013
  3. Betof AS, Dewhirst MW, Jones LW: Effects and potential mechanisms of exercise training on cancer progression: a translational perspective. Brain Behav Immun 30 Suppl:S75-87, 2013
  4. Ballard-Barbash R, Friedenreich CM, Courneya KS, et al: Physical activity, biomarkers, and disease outcomes in cancer survivors: a systematic review. J Natl Cancer Inst 104:815-40, 2012