Cancer Prevention and Management through Exercise and Weight Control PDF

Preface

Many clinicians, researchers, and lay public associate an expanding waistline and a couch-potato lifestyle with increased tendency to develop cardiovascular disease and some of its risk factors (diabetes, hypertension, hypercholesterolemia). These lifestyle factors, however, also play into the etiology and prognosis of several types of cancers, which is important in the clinical and public health areas. It is important to public health because cancer is a common disease (one in two men and one in three women will develop cancer in their lifetime) and overweight or obesity and sedentary behavior are extremely common and becoming more so (two thirds of American adults are overweight or obese, and three quarters do not meet the minimal recommendations for 30 minutes of aerobic activity per day). It is important to medicine because a marked increase in a consistent risk factor will mean an increase in number of cancer cases unless some other widespread prevention factor negates this effect.

In addition, the implications for poorer prognosis in affected individuals means that treating oncologists and other health care providers will need to develop new and better therapies to deal with the declining prognosis in this large segment of the population. Clinicians should be aware that, because two thirds of the American population is overweight or obese and being overweight increases risk for cancer, the vast majority of cancers in the future will occur in overweight and obese individuals.

The association between obesity and a sedentary lifestyle with risk for cancer has been appreciated for several decades. Only in the past 10 years or so, however, has the strength and consistency of this association been apparent. This is largely due to two things: (1) the increase in prevalence in overweight, obesity, and sedentary lifestyles; and (2) an increase in the number of epidemiological studies focusing on these associations.

The American Cancer Society estimates that a third of all cancer deaths could be prevented through avoidance of obesity and sedentary lifestyles. The World Health Organization's International Agency for Research on Cancer estimates that 25 to 30% of several cancers could be prevented if individuals avoided lifetime weight gain and obesity and participated in regular physical activity. These same organizations and several clinical groups are now recognizing the important role that physical activity can play in improving quality of life in cancer patients and survivors. This area is new, so there is great need for a definitive textbook that provides the scientific background and evidence supporting these relationships, as well as clinical guidelines for bringing physical activity and weight control into cancer prevention and treatment practices throughout the world.

We are very fortunate to have a world-class roster of authors for this text. The chapter authors have been chosen because they are the top researchers in the field of obesity, physical activity, and cancer.

Section I focuses on the research methods used in assessing the associations between physical activity, energy balance, and cancer risk and prognosis. Observational epidemiological studies can provide important information about relationships among these variables. More definitive evidence of the effect of changing behaviors, with resulting change in level of adiposity and amount of energy expended, is provided through randomized clinical trials. Dr. Prentice, principal investigator of the Women's Health Initiative Clinical Coordinating Center and a world expert on nutrition and cancer describes the benefits and drawbacks of each of these study design methods.

The measurement of energy balance and physical activity are far from straightforward. Energy balance involves the interplay among energy intake, energy expenditure, and metabolic rate. Genetic, age, and gender factors also play an important role. Defining what exactly energy balance is and what aspects of excessive adiposity are most pertinent to cancer and determining how much physical activity a person is actually doing are all great challenges requiring the concerted input of measurement experts. Drs. Ainsworth and Coleman present the intricacies of exercise and physical activity measurement, and Dr. Irwin describes the pluses and minuses of the many ways of assessing body composition.

The role of physical activity in the incidence of individual cancers is the focus of Section II. In a comprehensive literature review, Drs. Patel and Bernstein write about the intriguing data pointing to a role of exercise and physical activity in reducing risk for breast cancer. They compare and contrast the types of epidemiological studies and the role of exercise and physical activity in premenopausal and postmenopausal breast cancer. The many studies on exercise, physical activity, and colon cancer are reviewed by Dr. Slattery, who summarizes how exercise plays a role in colon cancer etiology. She also reviews the evidence regarding the association between physical activity and rectal cancer occurrence. Dr. Friedenreich elegantly summarizes the state of knowledge on the associations between exercise and prostate cancer risk, pointing out why the associations are not yet firm and suggesting future research pathways.

Section III focuses on mechanisms that may explain the inverse association between physical activity and incidence of several cancers. Dr. McTiernan reviews the effect of exercise on sex hormones, which has relevance for several hormone-related cancers such as breast, endometrium, and prostate. Dr. Frank reviews the role of exercise in reducing insulin resistance and hyperinsulinemia; insulin has been shown to promote tumor cells in vitro, and persons with high insulin levels have increased risk for some cancers and reduced prognosis once diagnosed with breast cancer. Ms. Wetmore and Dr. Ulrich review the literature on the complicated associations between physical activity and several markers of immune function, especially ones that may be relevant to cancer occurrence or prognosis. Dr. Martínez describes the effect of exercise on prostaglandins, which may in part explain the consistent findings of reduced colon cancer risk among active, compared with sedentary, persons. Drs. Thompson, Jiang, and Zhu describe the animal model research that has defined the role of excess adiposity and of energy restriction on tumorogenesis. The current state of human intervention studies on physical activity and cancer biomarkers is presented by Dr. McTiernan. Dr. Rankinen reviews the intriguing new field of genetics, physical activity, and cancer, which may help to define persons who may be helped with activity in terms of cancer risk.

Section IV focuses on the breadth and depth of knowledge on the effect of overweight and obesity on cancer incidence. Dr. Ballard-Barbash presents the state of knowledge regarding the effects of weight, adiposity, lifetime weight change, and risk of breast cancer in premenopausal and postmenopausal women. Drs. Kaaks and Lukanova present similar information for the effect of increasing adiposity on the development of endometrial cancer. Drs. Michaud and Giovannucci present the emerging data linking increased adiposity with increased risk for pancreatic cancer. The new and increasing body of knowledge regarding the effect of obesity on esophageal cancer is presented by Drs. Hoyo and Gammon. Dr. Slattery reviews the role of overweight and obesity in the etiology of colon cancer.

Section V reviews the mechanisms that might explain the association between adiposity and incidence of several cancers. Drs. Kaaks and McTiernan describe the role of adipose tissue in the production and metabolism of sex hormones, which is important for several hormone-related cancers such as breast, endometrium, and prostate cancers. Dr. Blackburn presents the state of knowledge regarding obesity and insulin resistance, taking from the extensive depth of information available from diabetic research results. Drs. Priest and Church present data on the effect of adiposity on cytokines and inflammatory markers that may have particular relevance for cancer. The important role of animal studies in shedding light on the effect of exercise on biology related to cancer formation is described in depth by Dr. Colbert. Drs. Tworoger and McGrath present the emerging body of literature on the genetics of obesity as it pertains to cancer incidence.

Section VI concentrates on the importance of physical activity on aspects of quality of life and prognosis for many cancer patients. Dr. Winters-Stone describes the studies that have examined the effect of exercise and physical activity on fatigue in breast cancer patients and survivors. Dr. Courneya, Ms. Campbell, Ms. Karvinen, and Ms. Ladha describe studies that have explored the effect of exercise on quality of life in colon and other cancer patients. Drs. Abrahamson and Gammon describe the emerging information on the role of physical activity in cancer prognosis and suggest biological mechanisms that might explain the association.

Section VII presents information on the role of overweight and obesity on prognosis of several cancers. Dr. Goodwin reviews the many studies that have examined the effect of adiposity on breast cancer recurrence and survival and presents suggested mechanisms for such relationships. Dr. Rock presents results of recent studies pointing to a role of adiposity on survival and recurrence in patients with colon, prostate, and other cancers.

The final section, Section VIII, gives the reader clues to how the information presented in the rest of the book might be implemented at the individual, clinical, and public health levels. Dr. Fogelholm writes on the use of exercise and physical activity in weight control at the individual level. Dr. Heber and Ms. Bowerman provide information on dietary and other methods of energy balance for overweight and obese persons. Dr. Bull describes population-level initiatives to increase physical activity in population settings. Dr. Pronk provides insight into disseminating exercise and diet interventions into the primary care setting. Drs. Schwartz and Winters-Stone provide advice on initiating and maintaining increased exercise and physical activity in cancer patients and survivors. Finally, Drs. Chlebowski, Geller, Harvie and Howell provide guidance on incorporating exercise and diet recommendations into clinical oncology practice.

We hope that this volume provides a comprehensive review of the roles of energy balance, physical activity, and cancer incidence and prognosis. The epidemic of overweight and obesity and the increasing prevalence of sedentary lifestyles will have an impact on the magnitude and quality of the cancer problem around the globe. Viewed differently, knowing that energy balance is so important to the risk and prognosis from cancer may be an important incentive for the general public, persons at high risk, and cancer patients and survivors to increase physical activity, reduce excess weight, and maintain energy balance lifelong.