Thanks to earlier detection and better, targeted, and multimodal cancer treatment, many individuals diagnosed with cancer can now expect to live for years beyond their treatment. Recent data have demonstrated that an estimated 28 million individuals worldwide had a history of cancer as of 2008, the most recent year for which worldwide data are available. That number represents 5-year prevalence, so it is a dramatic underestimate of the total number of cancer survivors. Furthermore, the number of cancer survivors will increase significantly in the coming years with the aging of the Baby Boomer generation (those born from 1946 to 1964). For example, in the United States alone, it is estimated that there will be over 18 million survivors by 2022, 11 million of whom will be older adults.
Although the increase in the number of cancer survivors is good news, it also means that more individuals than ever before are living with the chronic and late effects of cancer treatment. Chronic effects are problems present during treatment that may persist for months or years after treatment and include fatigue; neuropathy and pain syndromes; depression, anxiety, and distress; lymphedema; problems with cognition; incontinence; altered body image; and sexual dysfunction. Late effects are not present during treatment but emerge during the post-treatment period and include cardiovascular disease; endocrine dysfunction; diabetes; osteoporosis; upper or lower quadrant mobility issues and functional limitations; and increased risk of recurrence, second cancers, and disability. Research attention in the last 15 years on both sides of the Atlantic has focused on identifying risk factors for physical and psychosocial chronic and late effects of cancer treatment and on developing and testing interventions to prevent or reduce the risk of these negative sequelae. One important line of this research has focused on the role of obesity and energy balance, as determined by dietary intake and energy expenditure, in determining the risk of chronic and late effects and the role that interventions to promote exercise and a healthy body weight may play in mitigating these problems.
Worldwide, physical inactivity and obesity are common. In the United States, >33% of adults are obese, and another 33% are considered overweight. Fifty-three percent of US men and 60% of women do not engage in recommended levels of physical activity, whereas >33% of adults are considered inactive. Rates of obesity[6, 7] and inactivity are slightly better in Canada than in the United States. In Europe, the prevalence of obesity varies by country from 4% to 37%, and the prevalence is lower in the western and northern regions and is more akin to US estimates in the eastern, central, and southern areas. The prevalence of inactivity in Europe also differs by country, with Sweden, Finland, Austria, Ireland, and the Netherlands reporting lower levels of inactivity than the United States and Belgium and Mediterranean countries reporting inactivity levels equivalent to those in the United States.
Cancer, inactivity, and obesity also are related. Physical inactivity and obesity are associated with an increased risk of many cancers and with an increased risk of cancer progression and poor prognosis. Preclinical studies have suggested that excess body weight and inactivity may affect cell growth, differentiation, and apoptosis to promote primary tumor growth and also affect tissue invasion and angiogenesis, leading to tumor progression. Compounding the problem of cancer survivors being likely to be obese and inactive, individuals diagnosed with cancer often decrease their physical activity levels, eat poor-quality diets, and gain weight over the course of treatment, as noted especially among breast cancer survivors.[13, 14] The result of these factors is that the weight gain tends to be gains in fat mass with a corresponding loss of lean (muscle) mass. This problem, called sarcopenic obesity, may adversely affect the risk of chronic and late effects and poor prognosis.
For this commentary, our objective was to describe the similarities and differences in research and clinical priorities related to energy balance interventions among post-treatment cancer survivors in Europe versus North America. This was not intended to be an exhaustive review of these topics but, rather, a tool to initiate an international dialogue about these issues, which we hope will lead to better science and care for cancer survivors worldwide. We focus here on physical activity, weight, and diet as they contribute to obesity and sarcopenic obesity, but we do not cover the immense research on dietary components, isolates, or supplements and cancer. We present the problem of body composition changes among survivors as 2 sides of the same coin: greater overall body weight and/or elevated body mass index (BMI) values, which can obscure the presence of muscle wasting/cachexia.
Randomized, Controlled Trials Targeting Nutrition, Exercise, and Weight to Affect Survivorship Outcomes
The last 5 years have brought a considerable increase in the number of studies that develop and test interventions aimed at helping survivors to improve their exercise or diet or to lose weight. Most of these studies have been conducted in the United States or Canada, perhaps because of the increased prevalence of obesity and inactivity there, but the reasons for the greater interest here are unknown. Some of these studies have been “proof-of-concept” studies, ie, testing whether the intervention in fact does improve physical activity or reduce weight. However, a growing body of work has targeted survivorship outcomes, aiming to improve quality of life, reduce chronic effects of treatment, improve specific aspects of physical functioning, or reduce the risk of late effects of cancer.
Systematic reviews and meta-analyses of the literature on physical activity interventions for cancer survivors have indicated that these interventions significantly reduce depression[15-17] and fatigue[16-25] and improve cardiorespiratory fitness, muscle strength, body composition and physical functioning,[17, 22-26] body image,and quality of life.[16, 17, 24-27] Resistance training can improve cardiopulmonary and muscle function, peak oxygen uptake, strength,and quality of life. It is noteworthy that weight training has been shown to increase muscle mass and decrease body fat, thereby improving sarcopenic obesity. Exercise interventions that include strength training also may preserve bone health in cancer survivors. Indeed, the available evidence demonstrates that exercise is 1 of the most important therapies to improve functioning and quality of life of cancer survivors. In contrast to the recent burgeoning number of exercise trials, trials are just beginning to evaluate weight loss among cancer survivors. These interventions have been conducted almost exclusively among women with breast cancer. A recent review of this literature suggests that weight loss interventions may improve body composition (especially when combined with exercise), physical functioning, and quality of life.
Another major focus of research in the last 10 years has been investigating the role of energy balance in the risk of lymphedema (LE) and the role of exercise and weight loss interventions in reducing the risk or exacerbations of LE. LE, which can occur after surgery for breast cancer and for other malignancies, has major physical consequences (discomfort, swelling, increased risk for infections and secondary malignancies) and psychological consequences (depression, body image disorders) that can decrease quality of life and may affect survival. In most patients (approximately 75%), LE develops within 1 year of breast surgery; however, because of its insidious onset, LE carries a lifetime risk for breast cancer survivors. It has been widely recognized that preoperative BMI increases the risk of LE,[34-37] with BMI values >30 kg/m2 doubling the risk. Despite the well established relation between preoperative overweight and postoperative risk of LE, few studies have evaluated the role of body weight reduction with either reduced-energy diets or exercise on the risk of developing or exacerbating LE in breast cancer survivors. Two British studies of breast cancer survivors demonstrated that weight loss through hypocaloric or low-fat diet can significantly reduce breast cancer-related LE.[39, 40] A review of strength training studies conducted with survivors who had LE demonstrated that slowly progressive strength training was safe and did not exacerbate LE symptoms. It has been observed that strength training interventions in the United States decreased the severity and exacerbations of LE symptoms among breast cancer survivors and decreased the likelihood of increased arm swelling among women at high risk for LE. In summary, the role of weight loss, physical exercise, dietary restrictions, and nutritional counseling in the prevention or control of LE in long-term breast cancer survivors remains largely unexplored both in the United States and in Europe, underscoring the urgent need for large multicenter trials addressing this relevant clinical issue.
Interventions Focused on Improving Prognosis/Survival
Whether exercise and/or weight loss may favorably influence prognosis or overall survival is a matter of great interest in North America. Such trials must include large sample sizes and lengthy follow-up periods; thus, they have not been completed to date. However, a study funded by The National Cancer Institute of Canada is currently conducting a survival trial testing whether exercise can favorably influence disease-free survival among individuals diagnosed with higher risk colorectal cancer (the Colon Health and Life-Long Exercise Change [CHALLENGE] trial). A study testing the effects of weight loss on survival from estrogen receptor-positive breast cancer (Lifestyle Intervention Study in Adjuvant Treatment of Early Breast Cancer [LISA]; P. Goodwin, principal investigator; clinicaltrials.gov identifier NCT00463489) also was being conducted in Canada; however, that study was terminated early because of lost funding.
Two diet intervention studies among breast cancer survivors in the United States have been carried out. The Women's Intervention Nutrition Study (WINS) tested the effects of a low-fat diet among 2437 women with early stage breast cancer on relapse. An interim analysis conducted with 5 years of follow-up revealed marginally significantly lower relapse-free survival in the low-fat diet arm, and subgroup analyses indicated a significantly lower relapse rate among women who had estrogen receptor-negative breast cancers. However, it is not known whether these effects were because of the low-fat diet or because of the average 6-pound weight loss experienced by women in the intervention group. The Women's Healthy Eating and Living (WHEL) study tested the effects of a low-fat, high fruit and vegetable/fiber diet on cancer outcomes in 3088 women with breast cancer. Women in the intervention arm reduced their fat intake but did not lose weight, and there was no difference between the intervention and control arms in recurrence-free survival. However, subgroup analyses revealed that prognosis was improved among women in the intervention group who did not report hot flashes (who likely had higher circulating estrogen levels).
Interventions Focused on Improving Biomarkers of Prognosis or Survival
In the absence of trials targeting survival, some investigators in the United States and Canada have begun to investigate whether physical activity, diet, or weight change can favorably influence intermediate biomarkers of prognosis/survival, including sex hormones, insulin or insulin-like growth factors or their binding proteins, insulin resistance, glucose metabolism, leptin and other adipokines, immunologic or inflammatory factors, oxidative stress and DNA damage or repair capacity, angiogenesis, or prostaglandins. For example, Pakiz et al investigated the effect of a weight loss intervention (regular physical activity and reduced energy intake) on inflammation and vascular endothelial growth factor in overweight or obese breast cancer survivors. Weight loss was associated with reduced cytokine levels, and increased energy expenditure was associated with a significant reduction in circulating levels of interleukin-6. Befort et al demonstrated that a low-calorie diet and physical activity reduced body weight and improved fasting insulin and leptin levels in rural American breast cancer survivors. Allgayer and colleagues in Germany documented the effects of exercise on DNA damage and inflammation in colorectal cancer survivors (for a complete summary, please see recent reviews of this emerging literature[52, 53] and the recent US Institute of Medicine report on this topic). It is noteworthy that, although this has been a topic of emphasis in North America, aside from the work by Allgayer et al cited above and a recently closed clinical trial in the United Kingdom, it has not been a priority among European investigators. Future studies are needed to clarify the role of weight loss and physical activity on biomarkers of prognosis or survival among cancer survivors, including the dose and type of these interventions needed to garner protective effects.
Guidelines and Care Implications
The American Cancer Society (ACS) provides guidelines on nutrition and physical activity for cancer survivors. These guidelines state that, during the post-treatment phase, setting and achieving life-long goals for weight management, a physically active lifestyle, and a healthy diet are important tools to promote overall health and quality and quantity of life. These guidelines are based on the consideration that individuals who have been diagnosed with cancer are at a significantly higher risk of developing second primary cancers and chronic diseases, such as cardiovascular disease, diabetes, and osteoporosis; thus, the guidelines established to prevent those diseases are relevant. In brief, the ACS guidelines advise survivors to achieve and maintain a healthy weight. Overweight or obese survivors should limit consumption of high-calorie foods and beverages and should increase their physical activity to promote weight loss. All survivors should engage in regular physical activity; should avoid inactivity, aiming to exercise at least 150 minutes per week, including strength training exercises at least 2 days per week; and should eat a diet high in vegetables, fruits, and whole grains. These guidelines are consistent with the ACS Guidelines on Nutrition and Physical Activity for Cancer Prevention for the general population. The American College of Sports Medicine Roundtable on Exercise Guidelines for Cancer Survivors echoes the ACS guidelines, stating that current national exercise guidelines for the US population are appropriate for cancer survivors.
The National Cancer Survivorship Initiative-Supported Self-Management Workstream developed in 2010 in the United Kingdom (Department of Health, Macmillan Cancer Support, National Health Service Improvement, 2010) aimed at updating the World Cancer Research Fund (WCRF) report's guidelines. Although the authors recognize gaps in the evidence for lifestyle benefits in cancer survivors, some key lifestyle general recommendations are provided regarding diet (reduce saturated fats, increase fish intake, and consume a varied diet to ensure adequate intakes of vitamins and essential minerals; increase consumption of green and cruciferous vegetables, etc.) and physical activity (at least 30 minutes a day of moderate-intensity physical activity on 5 or more days of the week, although even a modest amount of exercise is considered beneficial and, thus, is encouraged). The role of body composition changes that occur in many cancer patients, depending on tumor localization and treatments, is also emphasized. In particular, the loss of lean body mass (sarcopenia) for patients with head and neck and gastrointestinal cancers is highlighted, and physical exercise is suggested to build lean muscle and prevent post-treatment disability, loss of autonomy, and impaired quality of life. In breast cancer patients, exercise/activity is suggested for controlling body weight and losing fat to combat treatment-related weight gain (which is exacerbated if the prediagnosis BMI is not within the healthy range). Excess weight should be avoided. The recommendation is also given to maintain a stable, healthy weight as opposed to fluctuating between a healthy and unhealthy BMI. Like the US exercise guidelines, the British Association of Sport and Exercise Sciences provides guidance on exercise for cancer survivors, indicating that survivors should follow health-related physical activity guidelines for the general United Kingdom population.
Along with its role in the achievement of energy balance and maintenance of healthy body weight, regular physical exercise should be encouraged to prevent or counteract the loss of muscle mass and function (ie, sarcopenia) that frequently complicates cancer and its therapies. Although it occurs most frequently during the phase of active disease and treatments and in advanced cancer, sarcopenia and the consequent functional impairment may represent a life-long disability for cancer survivors; thus, survivorship care needs to prevent, assess, and treat this debilitating condition. Permanent impairment in nutritional status secondary to medical or surgical cancer therapy ultimately may lead to skeletal muscle loss that interferes with everyday activities. Overall, little attention has been paid in both US and European guidelines to sarcopenia-related impairment in the quality of life of long-term cancer survivors. In this view, attention to body composition should be improved, because normal/elevated body weight or BMI may well mask an underlying, life-threatening sarcopenia.
Future Priorities for Research and Care Involving Energy Balance Among Survivors: European and American Perspectives
Meeting the needs of the growing population of cancer survivors requires the development of innovative models of care, which may be used to inform and enhance cancer survivorship care in different health care settings. The relevance of researching and optimizing the delivery of care to cancer survivors is being widely recognized in North America and is being progressively recognized in Europe. However, critically reviewing at the available literature, it is apparent that the American and European approaches to cancer survivorship both have pitfalls, particularly concerning noncancer-related health problems, such as promotion of healthy behaviors. Several specific issues have to be addressed and solved by future research in this field to build support for a model of comprehensive survivorship care that meets the needs of all survivors:
- Although current evidence from cohort and cross-sectional studies suggests that excess body weight and sarcopenic obesity are associated with increased risk of chronic and late effects of cancer, trials should test whether intentional weight loss among cancer survivors results in decreased risk of LE or late effects like cardiovascular disease. Both North American and European investigators have acknowledged this as a priority area.
- Current guidelines on prescribing exercise, nutrition, and weight control interventions for cancer survivors are based on general public health advice given to the general population. However, achieving the level of healthy behaviors set forth in these recommendations may not be effective for reducing morbidity and mortality among cancer survivors. Randomized clinical trials are needed to generate evidence-based guidelines for cancer survivors.
- A related direction concerns being able to prescribe appropriately targeted, individualized lifestyle recommendations for cancer survivors. On both sides of the Atlantic, there is interest in conducting trials that establish the intensity and type of intervention needed given an individual survivor's unique disease, psychosocial, behavioral, and genetic profile.
- The extent to which psychosocial issues like depression or diminished social support play a role in eating behavior and exercise after cancer treatment has received little attention in the literature on both sides of the Atlantic. For example, research should test whether ongoing psychosocial issues or effects of cancer treatments change the hormones that govern appetite (eg leptin, ghrelin).
- Given the demands of the cancer survivor population on the health care system and the projected dramatic increase in the number of cancer survivors in the future, trials are needed to establish a risk-stratification system for triaging survivors into appropriate levels of lifestyle interventions. For example, many survivors may be able to exercise safely without medical supervision. However, others may need intense oversight and targeted exercise prescription based on cardiovascular functioning parameters along the lines of current supervised cardiac rehabilitation programs in the United States. Investigators in the United States and the United Kingdom have begun work on this kind of risk stratification. More research is needed to identify those individuals who need different levels of lifestyle intervention and to guide the development and delivery of interventions.
- We need to focus on the promotion of long-term maintenance of healthy behavior changes. The few studies available on this topic suggest that survivors do not maintain their healthy behavior changes over time. Current interest in Europe and North America is focusing on how to keep individuals exercising, eating well, and avoiding weight regain once the intervention ends. For example, studies are investigating the predictors of maintaining behavior changes using behavioral theory.[63, 64]
- Another future direction concerns dissemination of these lifestyle interventions to all survivors who need them. Given the large geographic area of the United States, there is great interest in using technology and telemedicine approaches to increase the reach of behavioral change interventions to allow minorities and underserved populations to benefit from these interventions. For example, Morey and colleagues have observed that a home-based diet and exercise program using telephone counseling can reduce the rate of physical decline in at-risk cancer survivors. Befort and colleagues have used conference call technology to significantly decrease weight among overweight, rural breast cancer survivors. Similar initiatives are still lacking in Europe.
- A final area of emerging interest and debate in the United States concerns bariatric surgery for cancer survivors. Bariatric surgery can result in much greater weight loss than behavioral interventions and is associated with better maintenance of weight loss. Furthermore, bariatric surgery studies with the general population indicate that weight loss is associated with reductions in biomarkers of cancer prognosis. However, to date, studies have not addressed the safety and efficacy of bariatric surgery specifically in cancer survivors. In Europe, to our knowledge, there is not yet any discussion about whether bariatric surgery should be used for cancer survivors.
Research interests and priorities related to exercising, maintaining healthy weight, and losing weight in overweight and obese cancer survivors in Europe versus North America are more alike than different. Much of the research in this area has been conducted in North America, but a growing body of research also is being conducted in Europe. Where differences exist between the 2 continents, these are likely because of geographic-specific factors. For example, the interest in the areas of bariatric surgery for weight loss among very obese survivors and telemedicine approaches to delivering energy balance interventions to underserved communities in the United States but in not Europe likely reflects the larger obesity epidemic and greater geographic area of the United States. However, because current obesity trends in Europe suggest an imminent surge in the epidemic, and given the geographic variation between European Union countries (eg Northern and Southern Europe), it is likely these largely US-focused debates will be relevant to Europe in the near future.
Cancer survivors on both sides of the Atlantic face some of the same barriers to receiving adequate intervention programs to promote a healthy energy balance. Although this is changing now in the United Kingdom, for the most part, energy balance interventions are not delivered routinely on either continent as part of post-treatment survivorship care. The lack of a risk-stratification system makes it impossible for health care providers to know which survivors should be referred to which types of lifestyle interventions. Weight, diet, and exercise guidelines on both continents are based on guidelines for the general population and may not be sufficient to achieve optimal health and well being in certain subgroups of survivors. Finally, focus on the assessment of BMI but not body composition may be leading to missed diagnoses of sarcopenia and missed opportunities to prevent or ameliorate this debilitating condition. That these problems are universal underscores the need for international efforts to identify and implement their solutions. We hope that this dialogue launches an international conversation that will lead to better research and care for all post-treatment cancer survivors.