By Associate Professor Prue Cormie, Australian Catholic University for oncologynews.com.au
We all know that exercise is good for us but just how good is exercise for people with cancer?
This question has been addressed in a systematic review of over 100 research studies investigating the impact of exercise on the prognosis and wellbeing of people with cancer.
The findings of the research, which is the most comprehensive analysis of the available data in the field, support the view that exercise is an important adjunct therapy in the management of cancer. This view results from the observation that cancer patients involved in greater levels of exercise have a lower relative risk of cancer mortality, a lower relative risk of cancer recurrence, and they experience fewer and/or less severe treatment-related adverse effects.
What is the link between exercise and cancer survival?
This review synthesized mortality data from 36 studies investigating post diagnosis exercise levels in over 68,000 cancer patients. A consistent trend for reduced risk of cancer-specific mortality, cancer recurrence, and all-cause mortality was observed in patients who have superior exercise behaviours. Based on the 11 meta-analyses that have evaluated these outcomes to date, the magnitude of effect was observed to be considerable. Specifically, superior levels of exercise following a cancer diagnosis was associated with a 28-44% reduced relative risk of cancer-specific mortality, a 21-35% lower relative risk of cancer recurrence and a 25-48% decreased relative risk of all-cause mortality.
Given the nature of epidemiological investigations, this research is limited by the inability to infer direct causality between exercise behaviour and cancer outcomes. Thus, it is possible that observations of the protective effect of exercise may reflect reverse causality rather than a physiological effect. Specifically, better outcomes may be reported for more active patients because they are less encumbered by advanced or aggressive disease and/or severe symptomology rather than exercise induced adaptations that slow cancer progression.
However, the apparent protective effect of exercise was observed in multivariable adjusted analyses that account for a range of clinically relevant covariates associated with cancer progression (e.g. cancer stage, treatments, smoking status, BMI, co-morbidities etc.). Most evaluations to date have involved breast, colorectal and prostate cancer patients so it is currently unclear whether exercise is associated with improved disease outcomes in patients diagnosed with other types of cancer. Furthermore, insufficient data exists to determine if the degree of apparent protection varies according to cancer type, stage and/or treatment regimen.
What impact does exercise have on treatment-related side effects?
This synthesis of over 60 randomised controlled trials demonstrates strong evidence of exercise as an efficacious therapy to counteract cancer treatment-related side effects. Specifically, the review confirmed that exercise significantly counteracts cancer-related fatigue.
Even though it may seem counterintuitive, regular exercise has been demonstrated to reduce the persistent fatigue experienced by many cancer patients. Significant beneficial effect was also observed for the role of regular exercise in managing psychosocial health following a cancer diagnosis. Regular exercise helps counteract the distress, depression and stress commonly experienced by people with cancer.
The review of the literature confirmed the beneficial effect of exercise on quality of life, with appropriately prescribed exercise leading to significant improvements. Alongside these well-established effects, there were other treatment-related side effects for which the evidence for benefits of exercise are currently equivocal: bone health, sexual function, treatment related symptoms, bladder and bowel symptoms, and anaemia.
Additionally, there is promising evidence for the benefits of exercise on other treatment-related side effects but insufficient evidence to draw broad conclusions: body image, sleep quality, physical function, physical health and lymphedema. Further research is required to discern the effect of exercise on these factors and to elucidate the intervention elements that serve as the active ingredient to improve each of these adverse treatment-related effects.
What are the mechanisms driving these effects?
So how can exercise provide benefit across such a broad range of health outcomes? Exercise is an effective medicine because it improves the structure and function of most of the body’s systems simultaneously. In fact, there is no medication or treatment that can positively influence as many body systems as exercise can. As such, a range of potential factors may contribute to the therapeutic effect of exercise for cancer patients.
Exercise may reduce the risk of cancer mortality and recurrence by enhancing the ability of patients to physically tolerate greater dosages of cancer treatment. Exercise may reduce the rate and magnitude of anti-cancer therapy dose modifications by increasing functional capacity and attenuating the severity of treatment related side effects, therefore allowing for higher treatment completion rates.
Similarly, improved fitness has been associated with enhanced surgical outcomes including less complications and morbidity. There is also the possibility that exercise may improve the effectiveness of anti-cancer treatments by normalising the tumour microenvironment and potentially increasing transport of systemic therapies to cancer cells.
A range of biological mechanisms have been proposed to mediate the protective effect of exercise on cancer outcomes. Specifically, exercise may elicit positive changes in inflammation, immunity, oxidative stress as well as metabolic and sex hormones, all of which are factors believed to contribute to cancer progression. Emerging research suggests exercise induces epigenetic modifications that are concordant with health-enhancing phenotypic adaptations may also play a role in enhancing outcomes for cancer patients. Furthermore, regular exercise is an established prophylactic measure which reduces the risk of developing co-morbid conditions such as heart disease, hypertension, diabetes and osteoporosis. While these factors may represent some potential pathways, precise mechanisms underlying the protective effect of exercise on cancer outcomes are yet to be elucidated.
Implementation of exercise within cancer care
A considerable body of literature now exists that provides convincing evidence of the beneficial impact of exercise on disease and patient outcomes. As the majority of cancer patients don’t exercise regularly, there is great potential to improve outcomes for patients and potentially to reduce health system expenditure (i.e. reduce the need to manage/treat some adverse treatment-related effects) through improved implementation of exercise within cancer care. To realize this potential, strategies to further develop policy and practice beyond the general exercise guidelines currently available are required.
Providing access to effective, accessible and affordable exercise medicine for all people diagnosed with cancer would involve all health professionals involved in the treatment of people with cancer discussing exercise with their patients, recommending they adhere with exercise guidelines and referring to a qualified exercise physiologist.
Based on the level of evidence, cancer departments and treatment centres nationwide should incorporate exercise physiologists within the multidisciplinary team and have on-site exercise facilities where evidence-based programs are delivered. Pathways for transition into cancer-specific community-based best-practice exercise services are required to maximise the potential of long term exercise behaviour.
For the potential of exercise to be realized, considerable effort and efficient investment are required to strengthen current policy and practice in this area.
How much exercise is enough & how do I get my patients exercising?
All people with cancer should avoid inactivity and be as physically active as current abilities and conditions allow. For significant health benefits cancer patients need to progress towards at least 150 minutes of moderate-intensity aerobic exercise (e.g. 30 min brisk walk 5 days a week or cycling, swimming) each week and 2-3 resistance exercise (i.e. lifting weights) sessions each week involving moderate- to vigorous-intensity exercises targeting the major muscle groups.
Discussing exercise as an adjunct therapy with your patients and encouraging them to engage in regular exercise is a strong motivator for patients to exercise. Coupling this with a referral to an accredited exercise physiologist who has experience in cancer care is a critical step in helping your patients reach these exercise levels while maximising safety and therapeutic effect.
Accredited exercise physiologists provide exercise advice and prescriptions that can be delivered in hospital-, community- and home-based setting which are eligible for subsidies through Medicare and private health insurances. An online directory of accredited exercise physiologist is available here.
What’s the bottom line?
If people with cancer exercise regularly they will significantly reduce the severity of cancer symptoms, improve their wellbeing and potentially extend their survival. Effectively implementing exercise within the cancer treatment paradigm would contribute to a reduction in the burden of cancer.
Lead image credit: Prue Cormie