Effect of a 12-month exercise intervention on patterns of cellular proliferation in colonic crypts: a randomized controlled trial

Generalized Linear Models with Covariate Measurement Error and Zero-Inflated Surrogates

Epidemiological studies often encounter a challenge due to exposure measurement error when estimating an exposure-disease association. A surrogate variable may be available for the true unobserved exposure variable. However, zero-inflated data are encountered frequently in the surrogate variables. For example, many nutrient or physical activity measures may have a zero value (or a low detectable value) among a group of individuals. In this paper, we investigate regression analysis when the observed surrogates may have zero values among some individuals of the whole study cohort. A naive regression calibration without taking into account a probability mass of the surrogate variable at 0 (or a low detectable value) will be biased. We developed a regression calibration estimator which typically can have smaller biases than the naive regression calibration estimator. We propose an expected estimating equation estimator which is consistent under the zero-inflated surrogate regression model. Extensive simulations show that the proposed estimator performs well in terms of bias correction. These methods are applied to a physical activity intervention study.

Impact of a randomized weight loss trial on breast tissue markers in breast cancer survivors

Few trials have examined the effect of lifestyle behavioral interventions on tissue markers in patients with cancer. The purpose of this study was to examine the feasibility and impact of a 6-month weight loss intervention on breast tissue and serum biomarkers in women with breast cancer. Fifty-one women who completed breast cancer treatment and had a BMI ≥ 25.0 kg/m² were randomized to a weight loss intervention or usual care. Breast tissue biopsies, fasting blood draw and body composition were collected at baseline and 6 months, with between-group changes examined using analysis of covariance method. Baseline and post-intervention biopsies were conducted in 49 and 42 women, respectively, with pre- and post-epithelial tissue available from 25 tissue samples. Average 6-month weight loss was 6.7% for the weight loss group and 2.0% increase for the usual care group (p < 0.0001). At baseline, body fat and serum insulin levels were inversely associated with breast tissue insulin receptor levels and CD68 (p < 0.05). At 6 months, favorable changes were observed in serum leptin and adiponectin levels and tissue CD163 among women randomized to weight loss vs. adverse change in women randomized to usual care (p < 0.05). Breast tissue biopsies are feasible to collect in a clinical research setting among breast cancer survivors, with weight loss favorably impacting metabolic and inflammatory markers associated with breast cancer.

Exercise effects on DNA methylation in EVL, CDKN2A (p14, ARF), and ESR1 in colon tissue from healthy men and women

Physical activity reduces risk of colon cancer persons by 20-30%. Aberrant methylation patterns are common epigenetic alterations in colorectal adenomas and cancers, and play a role in cancer initiation and progression. Alterations have been identified in normal colon tissue potentially representing a "field cancerization" process, where the normal colon is primed for carcinogenesis. Here, we investigate methylation patterns in three genes -Ena/VASP-like (EVL), (CDKN2A (p14, ARF)), and Estrogen Receptor-1 (ESR1)-in normal colon tissue collected at baseline and 12-months from 202 sedentary men and women, 40-75 years, enrolled in a randomized controlled trial testing an exercise intervention vs. control (http://clinicaltrials.gov/show/NCT00668161). Participants were randomized to moderate-to-vigorous intensity exercise, 60 minutes/day, 6 days/week for 12 months, or usual lifestyle. Sigmoid colon biopsies were obtained at baseline and 12-months, DNA extracted, and bisulphite converted. Droplet digital methylation-specific PCR was performed for EVL, p14ARF, and ESR1. Generalized estimating equations modification of linear regression were used to model relationships between intervention effects and candidate gene methylation levels, adjusting for possible confounders.There were no statistically significant differences between methylation patterns at 12-months between exercisers and controls. ESR1 methylation patterns differed by sex: women -10.58% (exercisers) +11.10% (controls); men +5.54% (exercisers), -8.16% (controls); (P=0.05), adjusting for BMI and age. There were no statistically significant changes in methylation patterns in any gene stratified by change in VO₂max, or by minutes/week of exercise.While no statistically significant differences were found in gene methylation patterns comparing exercises vs. controls, 12-month exercise effects on ESR1 methylation differed by sex, warranting further study.

Risk prediction models for colorectal cancer: Evaluating the discrimination due to added biomarkers

Most risk prediction models for colorectal cancer (CRC) are based on questionnaires and show a modest discriminatory ability. Therefore, we aim to develop risk prediction models incorporating plasma biomarkers for CRC to improve discrimination. We assessed the predictivity of 11 biomarkers in 736 men in the Health Professionals Follow-up Study and 639 women in the Nurses' Health Study. We used stepwise logistic regression to examine whether a set of biomarkers improved the predictivity on the basis of predictors in the National Cancer Institute's (NCI) Colorectal Cancer Risk Assessment Tool. Model discrimination was assessed using C-statistics. Bootstrap with 500 randomly sampled replicates was used for internal validation. The models containing each biomarker generated a C-statistic ranging from 0.50 to 0.59 in men and 0.50 to 0.54 in women. The NCI model demonstrated a C-statistic (95% CI) of 0.67 (0.62-0.71) in men and 0.58 (0.54-0.63) in women. Through stepwise selection of biomarkers, the C-statistic increased to 0.70 (0.66-0.74) in men after adding growth/differentiation factor 15, total adiponectin, sex hormone binding globulin and tumor necrosis factor receptor superfamily member 1B (P for difference = 0.008); and increased to 0.62 (0.57-0.66) in women after further including insulin-like growth factor 1 and insulin-like growth factor-binding protein 3 (P for difference = .06). The NCI + selected biomarkers model was internally validated with a C-statistic (95% CI) of 0.73 (0.70-0.77) in men and 0.66 (0.61-0.70) in women. Circulating plasma biomarkers may improve the performance of risk factor-based prediction model for CRC.

Exercise and immunometabolic regulation in cancer

Unhealthful lifestyle factors, such as obesity, disrupt organismal homeostasis and accelerate cancer pathogenesis, partly through metabolic and immunological dysregulation. Exercise is a prototypical strategy that maintains and restores homeostasis at the organismal, tissue, cellular and molecular levels and can prevent or inhibit numerous disease conditions, including cancer. Here, we review unhealthful lifestyle factors that contribute to metabolic and immunological dysregulation and drive tumourigenesis, focusing on patient physiology (host)-tissue-tumour microenvironment interactions. We also discuss how exercise may influence distant tissue microenvironments, thereby improving tissue function through both metabolic and immunospecific pathways. Finally, we consider future directions that merit consideration in basic and clinical translational exercise studies.

American College of Sports Medicine Roundtable Report on Physical Activity, Sedentary Behavior, and Cancer Prevention and Control

INTRODUCTION

The American College of Sports Medicine convened an International Multidisciplinary Roundtable on Exercise and Cancer in March 2018 to evaluate and translate the evidence linking physical activity and cancer prevention, treatment, and control. This article discusses findings from the Roundtable in relation to the biologic and epidemiologic evidence for the role of physical activity in cancer prevention and survival.

RESULTS

The evidence supports that there are a number of biologically plausible mechanisms, whereby physical activity can influence cancer risk, and that physical activity is beneficial for the prevention of several types of cancer including breast, colon, endometrial, kidney, bladder, esophageal, and stomach. Minimizing time spent in sedentary behavior may also lower risk of endometrial, colon and lung cancers. Conversely, physical activity is associated with higher risk of melanoma, a serious form of skin cancer. Further, physical activity before and after a cancer diagnosis is also likely to be relevant for improved survival for those diagnosed with breast and colon cancer; with data suggesting that postdiagnosis physical activity provides greater mortality benefits than prediagnosis physical activity.

CONCLUSIONS

Collectively, there is consistent, compelling evidence that physical activity plays a role in preventing many types of cancer and for improving longevity among cancer survivors, although the evidence related to higher risk of melanoma demonstrates the importance of sun safe practices while being physically active. Together, these findings underscore the importance of physical activity in cancer prevention and control. Fitness and public health professionals and health care providers worldwide are encouraged to spread the message to the general population and cancer survivors to be physically active as their age, abilities, and cancer status will allow.

Revisiting the impact of lifestyle on colorectal cancer risk in a gender perspective

Colorectal cancer (CRC) is a leading cause of cancer-related mortality in the world. Patterns and trends in CRC incidence and mortality correlate with increasing adoption of Western lifestyles and with the overweight/obesity epidemic. Both genetic background and a range of modifiable environmental/lifestyle factors play a role in CRC etiology. Among these the links of body weight, dietary patterns and physical activity (PA) behavior with CRC risk are some of the strongest for any type of cancer, with a different impact in women and men. Nonetheless, gender disparities still represent a neglected aspect of CRC management. This review sheds light on gender-related association of obesity and different dietary/PA habits with CRC risk, highlighting the importance of lifestyle modifications in the prevention of this neoplastic disease. In this scenario, intervention studies are strongly recommended to define the most effective dietary/PA regimens for primary prevention of cancer in women and men.

Physical Activity in Cancer Prevention and Survival: A Systematic Review

PURPOSE

This article reviews and updates the evidence on the associations between physical activity and risk for cancer, and for mortality in persons with cancer, as presented in the 2018 Physical Activity Guidelines Advisory Committee Scientific Report.

METHODS

Systematic reviews of meta-analyses, systematic reviews, and pooled analyses were conducted through December 2016. An updated systematic review of such reports plus original research through February 2018 was conducted. This article also identifies future research needs.

RESULTS

In reviewing 45 reports comprising hundreds of epidemiologic studies with several million study participants, the report found strong evidence for an association between highest versus lowest physical activity levels and reduced risks of bladder, breast, colon, endometrial, esophageal adenocarcinoma, renal, and gastric cancers. Relative risk reductions ranged from approximately 10% to 20%. Based on 18 systematic reviews and meta-analyses, the report also found moderate or limited associations between greater amounts of physical activity and decreased all-cause and cancer-specific mortality in individuals with a diagnosis of breast, colorectal, or prostate cancer, with relative risk reductions ranging almost up to 40% to 50%. The updated search, with five meta-analyses and 25 source articles reviewed, confirmed these findings.

CONCLUSIONS

Levels of physical activity recommended in the 2018 Guidelines are associated with reduced risk and improved survival for several cancers. More research is needed to determine the associations between physical activity and incidence for less common cancers and associations with survival for other cancers. Future studies of cancer incidence and mortality should consider these associations for population subgroups, to determine dose-response relationships between physical activity and cancer risk and prognosis, and to establish mechanisms to explain these associations.

Differences in Serum Biomarkers Between Combined Glucosamine and Chondroitin Versus Celecoxib in a Randomized, Double-blind Trial in Osteoarthritis Patients

BACKGROUND

Non-steroidal anti-inflammatory drugs, e.g., celecoxib, are commonly used for inflammatory conditions, but can be associated with adverse effects. Combined glucosamine hydrochloride plus chondroitin sulfate (GH+CS) are commonly used for joint pain and have no known adverse effects. Evidence from in vitro, animal and human studies suggest that GH+CS have anti-inflammatory activity, among other mechanisms of action.

OBJECTIVE

We evaluated the effects of GH+CS versus celecoxib on a panel of 20 serum proteins involved in inflammation and other metabolic pathways.

METHODS

Samples were from a randomized, parallel, double-blind trial of pharmaceutical grade 1500 mg GH + 1200 mg CS (n=96) versus 200 mg celecoxib daily (n=93) for 6- months in knee osteoarthritis (OA) patients. Linear mixed models adjusted for age, sex, body mass index, baseline serum protein values, and rescue medicine use assessed the intervention effects of each treatment arm adjusting for multiple testing.

RESULTS

All serum proteins except WNT16 were lower after treatment with GH+CS, while about half increased after celecoxib. Serum IL-6 was significantly reduced (by 9%, P=0.001) after GH+CS, and satisfied the FDR<0.05 threshold. CCL20, CSF3, and WNT16 increased after celecoxib (by 7%, 9% and 9%, respectively, P<0.05), but these serum proteins were no longer statistically significant after controlling for multiple testing.

CONCLUSION

The results of this study using samples from a previously conducted trial in OA patients, demonstrate that GH+CS reduces circulating IL-6, an inflammatory cytokine, but is otherwise comparable to celecoxib with regard to effects on other circulating protein biomarkers.

Energy balance and gastrointestinal cancer: risk, interventions, outcomes and mechanisms

Obesity increases the risk of multiple gastrointestinal cancers and worsens disease outcomes. Conversely, strong inverse associations have emerged between physical activity and colon cancer and possibly other gastrointestinal malignancies. The effect of weight loss interventions - such as modifications of diet and/or physical activity or bariatric surgery - remains unclear in patients who are obese and have gastrointestinal cancer, although large clinical trials are underway. Human intervention studies have already shed light on potential mechanisms underlying the energy balance-cancer relationship, with preclinical models supporting emerging pathway effects. Central to interventions that reduce obesity or increase physical activity are pluripotent cancer-preventive effects (including reduced systemic and adipose tissue inflammation and angiogenesis, altered adipokine levels and improved insulin resistance) that directly interface with the hallmarks of cancer. Other mechanisms, such as DNA repair, oxidative stress and telomere length, immune function, effects on cancer stem cells and the microbiome, could also contribute to energy balance effects on gastrointestinal cancers. Although some mechanisms are well understood (for instance, systemic effects on inflammation and insulin signalling), other areas remain unclear. The current state of knowledge supports the need to better integrate mechanistic approaches with preclinical and human studies to develop effective, personalized diet and exercise interventions to reduce the burden of obesity on gastrointestinal cancer.

Cancer Risk Factor Knowledge Among Young Adults

Cancer is the second leading cause of death in the USA. Incidence and mortality rates for cancer have risen steadily and cost the healthcare system over $264 billion annually. Cancer risk can be reduced by restricting alcohol consumption, avoiding tobacco, eating a balanced diet, limiting sun exposure, exercising, and seeking routine cancer screenings. The purpose of this study is to examine cancer risk factor knowledge among college students. Researchers surveyed undergraduate and graduate students (n = 758) at a mid-sized public university in the Southeast about their knowledge regarding cancer risk factors including smoking, alcohol consumption, diet, obesity, hypertension, and human papillomavirus (HPV). Participants were mostly able to identify the association between cancers and health risk behaviors that have received widespread media coverage, are somewhat intuitive, or are salient to their life stage such as drinking, tanning, and smoking. Nearly all participants correctly reported exposure to ultraviolet (UV) rays, and smoking increased risk of developing skin and lung cancer, respectively. Most students correctly identified an increased risk of liver cancer associated with alcohol use but missed head/neck and breast cancer. However, knowledge of less publicized relationships was insufficient. The findings offer encouragement to public health professionals that campaigns have increased awareness of cancer risk. However, there were many relationships that revealed a lack of knowledge, and future campaigns can target lesser-known cancer risk relationships to reduce the personal tragedy and societal burden of cancer.

The Impact of Diet-Induced Weight Loss on Biomarkers for Colorectal Cancer: An Exploratory Study (INTERCEPT)

OBJECTIVE

The aim of this study was to explore the potential effects of diet-induced weight loss on molecular biomarkers of colorectal cancer risk in serum and colorectal tissue.

METHODS

This single-arm exploratory study included 20 adults with BMI ≥ 30 kg/m2 completing an 8-week, complete, low-energy liquid diet. Pre- and postintervention anthropometric measurements, fasting blood draws, and endoscopic examinations to procure colorectal biopsies were performed. Fasting insulin, glucose, insulinlike growth factor 1 (IGF-1), C-reactive protein (CRP), and blood lipids were measured in serum, and tissue markers of apoptosis (M30), colonocyte proliferation (Ki-67), and insulin signaling (phospho-mTOR) were assessed using immunohistochemical staining.

RESULTS

Participants achieved substantial weight loss (mean = 13.56%). Mean concentrations of insulin, glucose, and cholesterol were significantly reduced (P < 0.05), but IGF-1 and CRP were not. Colorectal tissue expression of Ki-67 was significantly reduced (preintervention mean score = 7, postintervention mean score = 3.9, mean % change -43.8; P = 0.027). There were no significant changes in M30 or phospho-mTOR.

CONCLUSIONS

Weight loss in individuals with obesity was associated with improvements in insulin sensitivity and blood lipid profiles and a significant reduction in tissue Ki-67 expression. This is one of the first studies to demonstrate potential cancer-relevant changes in colorectal tissue following weight loss achieved through diet.

Effects of a Mediterranean Diet Intervention on Anti- and Pro-Inflammatory Eicosanoids, Epithelial Proliferation, and Nuclear Morphology in Biopsies of Normal Colon Tissue

This randomized trial evaluated the effects of intervention with either a Healthy Eating or a Mediterranean diet on colon biomarkers in 120 healthy individuals at increased colon cancer risk. The hypothesis was that eicosanoids and markers of proliferation would be favorably affected by the Mediterranean diet. Colon epithelial biopsy tissues and blood samples were obtained at baseline and after 6 mo of intervention. Colonic eicosanoid concentrations were evaluated by HPLC-MS-MS, and measures of epithelial proliferation and nuclear morphology were evaluated by image analysis of biopsy sections. There was little change in proinflammatory eicosanoids and in plasma cytokine concentrations with either dietary intervention. There was, however, a 50% increase in colonic prostaglandin E3 (PGE3), which is formed from eicosapentanoic acid, in the Mediterranean arm. Unlike PGE2, PGE3, was not significantly affected by regular use of non-steroidal anti-inflammatory drugs at baseline, and normal weight subjects had significantly higher colon PGE3 than overweight or obese subjects. Increased proliferation in the colon at baseline, by Ki67 labeling, was associated with morphological features that defined smaller nuclei in the epithelial cells, lower colon leukotriene concentrations and higher plasma cytokine concentrations. Dietary intervention had little effect on measures of epithelial proliferation or of nuclear morphology. The increase in PGE3 with a Mediterranean diet indicates that in normal colon, diet might affect protective pathways to a greater extent than proinflammatory and proliferative pathways. Hence, biomarkers from cancer models might not be relevant in a true prevention setting.

Effects of physical activity on melatonin levels in previously sedentary men and women

BACKGROUND

The inverse association between physical activity and cancer risk may be mediated by higher melatonin levels. However, few studies have examined the effect of increased physical activity on melatonin levels.

METHODS

The parent study was a randomized controlled trial that randomized 51 men and 49 women to a 12-month moderate-to-vigorous aerobic exercise intervention ("exercisers") and 51 men and 51 women to a stretching control ("controls"). Participants were of ages 40 to 75 years, and previously sedentary. Levels of the principal urinary metabolite of melatonin, 6-sulfatoxymelatonin (aMT6s), corrected for creatinine levels, were measured in spot morning urine samples by immunoassay at baseline and 12 months. Changes in levels between exercisers and controls were compared using generalized estimating equations for linear regression.

RESULTS

We observed no statistically significant difference in the change in aMT6s levels from baseline to 12 months in exercisers compared with controls (change in aMT6s levels: exercisers, +6.5%; controls, +13%; P = 0.66). There was no evidence of effect modification by age, sex, or body mass index.

CONCLUSIONS

A 12-month moderate-intensity exercise intervention did not affect levels of aMT6s.

IMPACT

Further research needs to focus on other potential mechanisms through which physical activity may reduce the risk of cancer. Cancer Epidemiol Biomarkers Prev; 23(8); 1696-9. ©2014 AACR.

Ex vivo culture of primary human colonic tissue for studying transcriptional responses to 1α,25(OH)2 and 25(OH) vitamin D

1α,25-Dihydroxyvitamin D3 [1α,25(OH)2D3] is a steroid hormone derived from circulating 25(OH) vitamin D [25(OH)D] with chemopreventive effects in colorectal cancer. 1α,25(OH)2D3 acts through transcriptional mechanisms; however, our understanding of vitamin D transcriptional responses in the colon is derived from studies in transformed cancer cell lines which may not represent responses in normal healthy tissue. Here, we describe the optimization of an ex vivo culture model using primary colonic biopsy samples for studying short-term transcriptional response induced by 1α,25(OH)2D3 and 25(OH)D treatment. Colon biopsy samples from healthy subjects were maintained in primary culture and treated in parallel with 100 nM 1α,25(OH)2D3 or 62.5 nM 25(OH)D and vehicle control (ethanol). Viability was assessed using histology and enzymatic assays. Genome-wide transcriptional responses to 1α,25(OH)2D3 were assessed and expression of 25(OH)D targets CYP27B1 and CYP24A1 were measured by real time PCR. We show that ex vivo culture of colonic tissue remains viable for up to 8 h. The largest number of differentially expressed genes in response to 1α,25(OH)2D3 was noted after 6 h (n = 120). As proof of concept, the top upregulated gene was CYP24A1, a well-established vitamin D-responsive gene. With 25(OH)D treatment, mRNA expression of CYP27B1 was significantly increased after 1 h, while expression of CYP24A1 was greatest at 8 h. Ex vivo culture can be used to assess short-term transcriptional responses to 1α,25(OH)2D3 and 25(OH)D in primary tissue from human colon. Future studies will address interindividual differences in transcriptional responses.

Predicting adherence of adults to a 12-month exercise intervention

BACKGROUND

The purpose of this study was to (a) examine demographic, psychosocial, and physiological predictors of exercise adherence in a yearlong exercise intervention and (b) describe the trajectory of adherence over time.

METHODS

Participants were 51 men and 49 women aged 40 to 75 years. The supervised and home-based intervention consisted of 60 minutes/day, 6 days/ week of moderate-to-vigorous intensity exercise. Three adherence measures were used: (1) minutes/week, (2) MET-hours/week, and (3) change in cardiopulmonary fitness (VO2max). Predictors of adherence were determined separately by sex using mixed models and multivariable regression.

RESULTS

Participants performed 287 ± 98 minutes/week of moderate-to-vigorous activity with 71% adhering to at least 80% (288 minutes/week) of the prescription. Men adhered better than women (P < .001). Among women, adiposity-related variables were significantly related to poorer adherence on all 3 measures (P < .05). A less consistent pattern was observed among men but in follow-up analyses, adiposity was associated with fewer MET-hours/week of exercise. Social support, pain, and perceived benefits were predictive in some models. Men and nonobese women experienced peak adherence at 4 to 6 months, while obese women peaked during months 0 to 3.

CONCLUSIONS

When provided with supervision and support, previously sedentary men and women can achieve and maintain high levels of aerobic activity.

Enhanced visibility of colonic neoplasms using formulaic ratio imaging of native fluorescence

BACKGROUND AND OBJECTIVES

Colonoscopy is the preferred method for colon cancer screening, but can miss polyps and flat neoplasms with low color contrast. The objective was to develop a new autofluorescence method that improves image contrast of colonic neoplasms.

STUDY DESIGN/MATERIALS AND METHODS

We selected the three strongest native fluorescence signals and developed a novel method where fluorescence images are processed in a ratiometric formula to represent the likely cellular and structural changes associated with neoplasia. Native fluorescence images of fresh surgical specimens of the colon containing normal mucosa, polypoid and flat adenomas as well as adenocarcinoma were recorded using a prototype multi-spectral imager. Sixteen patients, with a mean age of 62 years (range 28-81) undergoing elective resection for colonic neoplasms were enrolled. High contrast images were seen with fluorescence from tryptophan (Tryp), flavin adenine dinucleotide (FAD) and collagen.

RESULTS

When the image intensity of Tryp was divided pixel by pixel, by the intensities of FAD and collagen, the resulting formulaic ratio (FR) images were of exceptionally high contrast. The FR images of adenomas and adenocarcinomas had increased Weber contrast.

CONCLUSIONS

FR imaging is a novel imaging process that represents the likely metabolic and structural changes in colonic neoplasia that produces images with remarkably high contrast.

Can exercise-related improvements in immunity influence cancer prevention and prognosis in the elderly?

Cancer incidence increases with advancing age. Over 60% of new cancers and 70% of cancer deaths occur in individuals aged 65 years or older. One factor that may contribute to this is immunosenescence - a canopy term that is used to describe age-related declines in the normal functioning of the immune system. There are multiple age-related deficits in both the innate and adaptive systems that may play a role in the increased incidence of cancer. These include decreased NK-cell function, impaired antigen uptake and presentation by monocytes and dendritic cells, an increase in 'inflammaging', a decline in the number of naïve T-cells able to respond to evolving tumor cells, and an increase in functionally exhausted senescent cells. There is consensus that habitual physical exercise can offer protection against certain types of cancer; however the evidence linking immunological mechanisms, exercise, and reduced cancer risk remain tentative. Multiple studies published over the last two decades suggest that exercise can mitigate the deleterious effects of age on immune function, thus increasing anti-cancer immunity. The potential ameliorative effect of exercise on these mechanisms include evidence that physical activity is able to stimulate greater NK-cell activity, enhance antigen-presentation, reduce inflammation, and prevent senescent cell accumulation in the elderly. Here we discuss the role played by the immune system in preventing and controlling cancer and how aging may retard these anti-cancer mechanisms. We also propose a pathway by which exercise-induced alterations in immunosenescence may decrease the incidence of cancer and help improve prognosis in cancer patients.

Physical activity, occupational sitting time, and colorectal cancer risk in the Netherlands cohort study

We investigated occupational energy expenditure and sitting time in the longest held job (in men only), nonoccupational physical activity, and former sports participation in relation to colorectal cancer endpoints. The Netherlands Cohort Study includes 120,852 participants who completed a self-administered questionnaire in 1986 when they were aged 55-69 years. By 2002, 1,819 male and 1,366 female colorectal cancer cases were available for case-cohort analyses. In men, higher occupational energy expenditure levels and fewer occupational sitting hours were associated with decreased hazard ratios for colon cancer, particularly distal colon cancer (occupational energy expenditure of ≥12 vs. <8 kJ/minute, hazard ratio (HR) = 0.71, 95% confidence interval (CI): 0.52, 0.97; P for trend = 0.01; occupational sitting hours of <2 vs. 6-8 hours/day, HR = 0.63, 95% CI: 0.48, 0.83; P for trend = 0.001). The median duration of the longest held job for male subcohort members was 29 years. Nonoccupational physical activity was inconsistently associated with colorectal cancer endpoints in men, and it was inversely associated with colon cancer in women, particularly distal colon cancer (>90 vs. ≤30 minutes/day, HR = 0.69, 95% CI: 0.50, 0.96; P for trend = 0.06), and rectal cancer (>90 vs. ≤30 minutes/day, HR = 0.59, 95% CI: 0.39, 0.90; P for trend = 0.02). In conclusion, regular long-term physical activity and fewer sitting hours may protect against colon cancer, particularly distal colon cancer; results for rectal cancer were mixed.

Tryptophan autofluorescence imaging of neoplasms of the human colon

Detection of flat neoplasia is a major challenge in colorectal cancer screening, as missed lesions can lead to the development of an unexpected 'incident' cancer prior to the subsequent endoscopy. The use of a tryptophan-related autofluorescence has been reported to be increased in murine intestinal dysplasia. The emission spectra of cells isolated from human adenocarcinoma and normal mucosa of the colon were studied and showed markedly greater emission intensity from cancerous cells compared to cells obtained from the surrounding normal mucosa. A proto-type multispectral imaging system optimized for ultraviolet macroscopic imaging of tissue was used to obtain autofluorescence images of surgical specimens of colonic neoplasms and normal mucosa after resection. Fluorescence images did not display the expected greater emission from the tumor as compared to the normal mucosa, most probably due to increased optical absorption and scattering in the tumors. Increased fluorescence intensity in neoplasms was observed however, once fluorescence images were corrected using reflectance images. Tryptophan fluorescence alone may be useful in differentiating normal and cancerous cells, while in tissues its autofluorescence image divided by green reflectance may be useful in displaying neoplasms.

Effect of cyclooxygenase genotype and dietary fish oil on colonic eicosanoids in mice

Dietary ω3 fatty acids can modulate substrate availability for cyclooxygenases (COXs) and lipoxygenases, thus modulating downstream eicosanoid formation. This could be an alternative approach to using nonsteroidal anti-inflammatory drugs and other COX inhibitors for limiting Prostaglandin E(2) (PGE(2)) synthesis in colon cancer prevention. The aims of this study were to evaluate to what extent COX- and lipoxygenase-derived products could be modulated by dietary fish oil in normal colonic mucosa and to evaluate the role of COX-1 and COX-2 in the formation of these products. Mice (wild-type, COX-1 null or COX-2 null) were fed a diet supplying a broad mixture of fatty acids present in European/American diets, supplemented with either olive oil (oleate control diet) or menhaden (fish) oil ad libitum for 9-11 weeks. Colonic eicosanoid levels were measured by liquid chromatography tandem mass spectroscopy (LC-MS/MS), and proliferation was assessed by Ki67 immunohistochemistry. For the dietary alteration of colonic arachidonic acid: eicosapentaenoic ratios resulted in large shifts in formation of COX and lipoxygenase metabolites. COX-1 knockout virtually abolished PGE(2) formation, but interestingly, 12-hydroxyeicosatetraenoic (12-HETE) acid and 15-HETE formation was increased. The large changes in eicosanoid profiles were accompanied by relatively small changes in colonic crypt proliferation, but such changes in eicosanoid formation might have greater biological impact upon carcinogen challenge. These results indicate that in normal colon, inhibition of COX-2 would have little effect on reducing PGE(2) levels.

Reduced mitogenicity of sera following weight loss in premenopausal women

We investigated whether serum from normal weight women is less mitogenic and more apoptotic than sera from the same women in the overweight state. Sera from premenopausal women, age (mean ± SEE) 34.6 ± 0.53 years, who were randomized to caloric restriction (CR) (n = 13), CR + aerobic exercise (AE) (n = 14), or CR + resistance training (RT) (n = 20) were used to culture endometrial cancer cells. Phases of the cell cycle were determined, and proliferating cell nuclear antigen (PCNA) positivity was used to assess proliferation and apoptosis was assessed by determining cleaved caspase-3 and poly-ADP-ribose polymerase (PARP). Analyses showed that overall, cells grown in sera from the weight-reduced state had significantly more cells in G0/G1 and significantly fewer cells in the S and G2/M phases of the cell cycle than cells grown in sera from the overweight state. PCNA staining confirmed that cells grown in sera from the weight-reduced state had fewer proliferating cells. Cleaved caspase-3 and PARP were not different in cells grown in sera from the weight-reduced state compared to the overweight state. We conclude that weight loss with or without exercise could lower the risk for cancer through changes in serum that result in reduced cellular mitogenicity.

Effects of 12-month exercise on health-related quality of life: a randomized controlled trial

OBJECTIVE

We investigated exercise effects on health-related quality of life (HRQOL) and exercise self-efficacy, and tested effect modification by baseline body mass index (BMI) and gender.

METHODS

Middle-aged women (n=100) and men (n=102) were randomly assigned to either exercise (360 min/week of moderate-to-vigorous aerobic exercise) or control in Seattle, WA, from 2001 to 2004. Demographics, anthropometrics, exercise self-efficacy (5-item self-efficacy questionnaire) and HRQOL (SF-36) were assessed at baseline and 12 months. Analysis of covariance adjusting for baseline scores was used to compare HRQOL and exercise self-efficacy scores between the exercise and control groups.

RESULTS

At 12 months, exercisers demonstrated higher exercise self-efficacy than controls (percent change from baseline: -6.5% vs. -15.0%, p < 0.01), without differences in HRQOL. Baseline BMI category and gender did not modify these effects. In exploratory analyses comparing exercisers and controls within subgroups defined by gender and BMI, 12-month HRQOL scores [role-physical (+7.0% vs. -13.1%), vitality (+15.6% vs. -4.2%), social functioning (+10.0% vs. -3.5%), and mental health (+6.8% vs. -2.9%)] were higher only among overweight male exercisers (p < 0.05, vs. control).

CONCLUSION

Three hundred and sixty minutes per week of exercise, recommended for weight maintenance, did not have negative effects on exercise self-efficacy or HRQOL. This level of exercise may increase HRQOL among overweight men.

Physical activity and cancer prevention: a systematic review of clinical trials

BACKGROUND

Physically active individuals have lower rates of many cancers and improved cancer outcomes. Controlled exercise trials measuring putative biomarkers of cancer risk are being conducted to further understand the role of exercise in cancer etiology and progression. We aimed to systematically review the effect of exercise on various biomarkers.

METHODS

A comprehensive search strategy identified 353 publications from January 1980 to August 2010. We included those clinical trials of exercise measuring biomarkers following minimum 4-week intervention among cancer survivors or people with one or more cancer risk factors. Two reviewers abstracted data and assessed quality independently. Effect sizes and 95% confidence intervals were estimated.

RESULTS

Four primary prevention and five tertiary prevention trials were included. Exercise had a small to moderate effect on improving concentrations of several blood biomarkers implicated in breast and colon cancer pathways including insulin, leptin, estrogens, and apoptosis regulation. In breast cancer survivors, exercise had a small to moderate effect on improving some biomarkers associated with prognosis including various insulin-like growth factor axis proteins, insulin, and inflammation; and a large effect on enhancing immune function.

CONCLUSION

Data are few, but there is some evidence to support the role of exercise in modulating various cancer pathways.

Exercise and the Prevention of Oesophageal Cancer (EPOC) study protocol: a randomized controlled trial of exercise versus stretching in males with Barrett's oesophagus

BACKGROUND

Chronic gastro-oesophageal reflux disease and excessive body fat are considered principal causes of Barrett's oesophagus (a metaplastic change in the cells lining the oesophagus) and its neoplastic progression, oesophageal adenocarcinoma. Metabolic disturbances including altered levels of obesity-related cytokines, chronic inflammation and insulin resistance have also been associated with oesophageal cancer development, especially in males. Physical activity may have the potential to abrogate metabolic disturbances in males with Barrett's oesophagus and elicit beneficial reductions in body fat and gastro-oesophageal reflux symptoms. Thus, exercise may be an effective intervention in reducing oesophageal adenocarcinoma risk. However, to date this hypothesis remains untested.The 'Exercise and the Prevention of Oesophageal Cancer Study' will determine whether 24 weeks of exercise training will lead to alterations in risk factors or biomarkers for oesophageal adenocarcinoma in males with Barrett's oesophagus. Our primary outcomes are serum concentrations of leptin, adiponectin, tumour necrosis factor-alpha, C-reactive protein and interleukin-6 as well as insulin resistance. Body composition, gastro-oesophageal reflux disease symptoms, cardiovascular fitness and muscular strength will also be assessed as secondary outcomes.

METHODS/DESIGN

A randomized controlled trial of 80 overweight or obese, inactive males with Barrett's oesophagus will be conducted in Brisbane, Australia. Participants will be randomized to an intervention arm (60 minutes of moderate-intensity aerobic and resistance training, five days per week) or a control arm (45 minutes of stretching, five days per week) for 24 weeks. Primary and secondary endpoints will be measured at baseline (week 0), midpoint (week 12) and at the end of the intervention (week 24).

DISCUSSION

Due to the increasing incidence and very high mortality associated with oesophageal adenocarcinoma, interventions effective in preventing the progression of Barrett's oesophagus are urgently needed. We propose that exercise may be successful in reducing oesophageal adenocarcinoma risk. This primary prevention trial will also provide information on whether the protective association between physical activity and cancer is causal.

TRIAL REGISTRATION

ACTRN12609000401257.

The Colon Health and Life-Long Exercise Change trial: a randomized trial of the National Cancer Institute of Canada Clinical Trials Group

Background

Observational studies indicate that physical activity (pa) is strongly associated with improved disease outcomes in colon cancer survivors, but a randomized controlled trial is needed to determine whether the association is causal and whether new policies to promote exercise are justified.

Purpose

The co.21 Colon Health and Life-Long Exercise Change (challenge) trial undertaken by the National Cancer Institute of Canada Clinical Trials Group (ncic ctg) is designed to determine the effects of a structured pa intervention on outcomes for survivors of high-risk stage ii or iii colon cancer who have completed adjuvant therapy within the previous 2–6 months.

Methods

Trial participants (n = 962) will be stratified by centre, disease stage, body mass index, and performance status, and will be randomly assigned to a structured pa intervention or to general health education materials. The pa intervention will consist of a behavioural support program and supervised pa sessions delivered over a 3-year period, beginning with regular face-to-face sessions and tapering to less frequent face-to-face or telephone sessions. The primary endpoint is disease-free survival. Important secondary endpoints include multiple patient-reported outcomes, objective physical functioning, biologic correlative markers, and an economic analysis.

Summary

Cancer survivors and cancer care professionals are interested in the potential role of PA to improve multiple disease-related outcomes, but a randomized controlled trial is needed to provide compelling evidence to justify changes in health care policies and practice.

Physical activity and gastrointestinal cancer prevention

Colorectal cancer is the third most common cancer globally and is a leading cause of cancer death. Gastric cancer contributes significantly to the global cancer burden, particularly in low- and middle-income countries. We reviewed the literature for studies on physical activity or exercise and colon, rectal, and gastric cancers as well as colonic adenomatous polyps. We identified 52 studies of colon cancer, 31 studies of rectal cancer, 23 studies of colon polyps, and 16 studies of gastric cancer. Of the 52 studies of physical activity and colon cancer, 37 found a statistically significant association between increased levels of physical activity and decreased colon cancer risk in at least one comparison. Accumulated evidence suggests that physical activity is associated with a 25% reduction in colon cancer risk. In line with previous reports, we found no indication that the association was more pronounced for occupational versus recreational physical activity, with both resulting in a risk reduction of about 22%. Evidence for other domains of physical activity (i.e., transportation or household physical activity) is limited. Evidence is emerging that individuals who are consistently active across the lifetime may obtain greater risk reductions than those who are only active in recent years. Despite consistent associations with colon cancer, evidence is more limited though suggestive that physical activity reduces risk of colon adenomas or adenoma recurrence. There is clear evidence that physical activity is not associated with rectal or gastric cancers.

Physical activity and colon cancer prevention: a meta-analysis

Although an inverse association between physical activity and risk of colon cancer is well established, a formal estimate of the magnitude of this risk reduction that includes recent studies is not available. This analysis examines the association by sex and study design, restricting analyses to studies where data for colon cancer alone were available. The authors reviewed published studies through June 2008 examining the association between physical activity and risk of colon cancer. Heterogeneity and publication bias were evaluated and random effects models used to estimate relative risks (RR). Differences by sex and study design were evaluated. A total of 52 studies were included. An inverse association between physical activity and colon cancer was found with an overall relative risk (RR) of 0.76 (95% confidence interval (CI): 0.72, 0.81). For men, the RR was 0.76 (95% CI: 0.71, 0.82); for women, this was little different, (RR=0.79, 95% CI: 0.71, 0.88). The findings from case-control studies were stronger (RR=0.69, 95% CI: 0.65, 0.74) than for cohort studies (RR=0.83, 95% CI: 0.78, 0.88). This study confirms previous studies reporting an inverse association between physical activity and colon cancer in both men and women, and provides quantitative estimates of the inverse association.

Lifestyle, genes, and cancer

It is estimated that almost 1.5 million people in the USA are diagnosed with cancer every year. However, due to the substantial effect of modifiable lifestyle factors on the most prevalent cancers, it has been estimated that 50% of cancer is preventable. Physical activity, weight loss, and a reduction in alcohol use can strongly be recommended for the reduction of breast cancer risk. Similarly, weight loss, physical activity, and cessation of tobacco use are important behavior changes to reduce colorectal cancer risk, along with the potential benefit for the reduction of red meat consumption and the increase in folic acid intake. Smoking cessation is still the most important prevention intervention for reducing lung cancer risk, but recent evidence indicates that increasing physical activity may also be an important prevention intervention for this disease. The potential benefit of lifestyle change to reduce prostate cancer risk is growing, with recent evidence indicating the importance of a diet rich in tomato-based foods and weight loss. Also, in the cancers for which there are established lifestyle risk factors, such as physical inactivity for breast cancer and obesity for colorectal cancer, there is emerging information on the role that genetics plays in interacting with these factors, as well as the interaction of combinations of lifestyle factors. Integration of genetic information into lifestyle factors can help to clarify the causal relationships between lifestyle and genetic factors and assist in better identifying cancer risk, ultimately leading to better-informed choices about effective methods to enhance health and prevent cancer.

The Translational Research Working Group developmental pathway for lifestyle alterations

The Translational Research Working Group (TRWG) was created as a national initiative to evaluate the current status of National Cancer Institute's investment in translational research and envision its future. The TRWG conceptualized translational research as a set of six developmental processes or pathways focused on various clinical goals. One of those pathways describes the development of lifestyle alterations, which can, variously, be recommended to prevent cancer, modify a patient's adherence and response to cancer treatment, ameliorate side effects of cancer treatments, or improve prognosis and quality of life in cancer patients and survivors. The lifestyle alteration pathway was conceived not as a comprehensive description of the corresponding real-world processes, but rather as a tool designed to facilitate movement of a candidate lifestyle alteration through the translational process up to the point where it could be handed off for definitive testing, when appropriate. This article discusses key issues associated with the development of lifestyle alterations in light of the pathway.

Short-term moderate exercise programs reduce oxidative DNA damage as determined by high-performance liquid chromatography-electrospray ionization-mass spectrometry in patients with colorectal carcinoma following primary treatment

OBJECTIVE

Oxidative DNA damage is believed to be involved in tumor formation and may be an important biomarker for malignant transition or relapse. A decrease of such damage has been observed in human and animal studies following dietary intervention and/or changes in lifestyle such as physical exercise at different levels of intensity. The purpose of this study was to carry out a clinical trial comparing the effects of a short-term (2 weeks) exercise program of moderate intensity (0.3-0.4 x maximal exercise capacity) (MI) versus high intensity (0.5-0.6 x maximal exercise capacity) (HI) on individual urinary excretion of 8-oxo-dG before and after completion of the exercise programs.

MATERIAL AND METHODS

In this short-term, prospective and randomized trial, 19 patients with colorectal cancer were allocated to the MI group following primary therapy and 29 to the HI group. Urinary 8-oxo-dG excretion concentration was determined by a highly sensitive detection method using high-performance liquid chromatography coupled to electrospray ionization mass spectrometry (HPLC-ESI-MS). Concentrations were determined immediately before and after completion of the exercise programs.

RESULTS

Using HPLC-ESI-MS, it was shown that MI exercise significantly reduced urinary 8-oxo-dG excretion levels from 8.47 +/- 1.99 to 5.81 +/- 1.45 (ng/mg creatinine, mean +/- SE, p = 0.02), whereas HI exercise resulted in a non-significant increase from 5.00 +/- 1.31 to 7.11 +/- 1.63 (ng/mg creatinine, p = 0.18). Clinical characteristics (gender, age, body mass index (BMI), diet, chemotherapy/irradiation) were not associated/correlated with urinary 8-oxo-dG levels.

CONCLUSIONS

By using HPLC-ESI-MS it was shown that short-term MI exercise after primary therapy in patients with colorectal cancer was associated with lower levels of urinary 8-oxo-dG, suggesting decreased oxidative DNA damage. In contrast, HI exercise tended to increase DNA damage. A prospective trial is now warranted to prove that reduced oxidative DNA damage lowers the risk of relapse of colorectal cancer in treated patients.

Exercise reduces inflammation and cell proliferation in rat colon carcinogenesis

PURPOSES

There is evidence that the risk of colon cancer is reduced by appropriate levels of physical exercise. Nevertheless, the mechanisms involved in this protective effect of exercise remain largely unknown. Inflammation is emerging as a unifying link between a range of environment exposures and neoplastic risk. The carcinogen dimethyl-hydrazine (DMH) induces an increase in epithelial cell proliferation and in the expression of the inflammation-related enzyme cyclooxigenase-2 (COX-2) in the colon of rats. Our aim was to verify whether these events could be attenuated by exercise.

METHODS

Four groups of eight Wistar rats were used in the experiment. The groups G1 and G3 were sedentary (controls), and the groups G2 and G4 were submitted to 8 wk of swimming training, 5 d.wk. The groups G3 and G4 were given subcutaneous injections of DMH immediately after the exercise protocols. Fifteen days after the neoplasic induction, the rats were sacrificed and the colon was processed for histological examination and immunohistochemistry staining of proliferating cell nuclear antigen (PCNA) and COX-2.

RESULTS

We found a significant increase in the PCNA-labeling index in both DMH-treated groups of rats. However, this increase was significantly attenuated in the training group G4 (P < 0.01). Similar results were observed in relation to the COX-2 expression.

CONCLUSIONS

From our findings, we conclude that exercise training exerts remarkable antiproliferative and antiinflammatory effects in the rat colonic mucosa, suggesting that this may be an important mechanism to explain how exercise protects against colonic cancer.

Effect of exercise on serum sex hormones in men: a 12-month randomized clinical trial

PURPOSE

The effect of exercise on androgens in middle-aged to older men is poorly understood, and it could have implications for several aspects of health. This analysis was conducted to examine the effects of long-term aerobic exercise on serum sex hormones in middle-aged to older men.

METHODS

One hundred two sedentary men, ages 40-75 yr, were randomly assigned to a 12-month exercise intervention or a control group (no change in activity). The combined facility- and home-based exercise program consisted of moderate/vigorous-intensity aerobic activity for 60 min.d(-1), 6 d.wk(-1). Serum concentrations of testosterone, free testosterone, dihydrotestosterone (DHT), 3alpha-androstanediol glucuronide (3alpha-Diol-G), estradiol, free estradiol, and sex hormone-binding globulin (SHBG) were measured at baseline, 3, and 12 months.

RESULTS

Exercisers trained a mean of 370 min.wk(-1) (102% of goal), with only two dropouts. Cardiopulmonary fitness (.VO(2max)) increased 10.8% in exercisers and decreased by 1.8% in controls (P < 0.001). DHT increased 14.5% in exercisers versus 1.7% in controls at 3 months (P = 0.04); at 12 months, it remained 8.6% above baseline in exercisers versus a 3.1% decrease in controls (P = 0.03). SHBG increased 14.3% in exercisers versus 5.7% in controls at 3 months (P = 0.04); at 12 months, it remained 8.9% above baseline in exercisers versus 4.0% in controls (P = 0.13). There were significant trends toward increasing DHT and SHBG, with greater increases in .VO(2max) at 3 and 12 months in exercisers. No statistically significant differences were observed for testosterone, free testosterone, 3alpha-Diol-G, estradiol, or free estradiol in exercisers versus controls.

CONCLUSIONS

A year-long, moderate-intensity aerobic exercise program increased DHT and SHBG, but it had no effect on other androgens in middle-aged to older men.

Physical activity before and after diagnosis of colorectal cancer: disease risk, clinical outcomes, response pathways and biomarkers

Physical inactivity may be responsible for 13-14% of colon cancer, an attributable risk greater than family history. Epidemiological evidence shows an association between occupational and recreational physical activity and colon cancer, but has not established whether physical activity is protective against low-risk or more advanced adenomas. The evidence is inconclusive as to whether physical activity protects against rectal cancer and is conflicting with respect to whether physical activity has equal effects on male and female risk of colorectal cancer. The effect of exercise 'interventions' on the risk of colorectal cancer is currently not known. Also, although inferences can be made from epidemiological studies, no optimal exercise regimen can be confidently prescribed for protection against colorectal cancer. There is little available evidence for the benefits of physical activity before diagnosis of colorectal cancer for disease-specific survival and prognosis, and the clinical effects of an exercise intervention after diagnosis have not been investigated. There is some evidence that improvements in cardiorespiratory fitness reduce adverse effects from cancer treatment when physical activity is undertaken following diagnosis of colorectal cancer. Markers/mechanisms by which physical activity may protect against colorectal cancer and/or improve disease prognosis include gastrointestinal transit-time, chronic inflammation, immune function, insulin levels, insulin-like growth factors, genetics and obesity. Research evidence is, however, limited as to whether these markers are beneficially affected by physical activity, either before or after diagnosis of colorectal cancer.

Effect of a 12-Month Exercise Intervention on the Apoptotic Regulating Proteins Bax and Bcl-2 in Colon Crypts: A Randomized Controlled Trial

BACKGROUND

Cellular proliferation and apoptosis (cell death) are highly regulated in the colon as insufficient apoptosis may lead to polyps and cancer. Physical activity decreases risk of colon cancer in observational studies, but the biological basis is not well defined. The objective of this study is to examine the effects of a 12-month aerobic exercise program on expression of proteins that promote (Bax) or inhibit (Bcl-2) apoptosis in colon crypts.

METHODS

Two hundred two sedentary participants, 40 to 75 years, were randomly assigned to moderate-to-vigorous intensity exercise for 60 min per day, 6 days per week for 12 months, or usual lifestyle. Colon crypt samples were obtained at baseline and 12 months. Bcl-2 and Bax expression was measured by immunohistochemistry.

RESULTS

Bax density at the bottom of crypts increased in male exercisers versus controls (+0.87 versus -0.18; P = 0.05), whereas the ratio of Bcl-2 to Bax at the bottom and middle of crypts decreased as aerobic fitness (VO(2)max) increased (P trend = 0.02 and 0.05, respectively). In female exercisers, Bax density in the middle of crypts decreased (-0.36 versus +0.69; P = 0.03) and Bcl-2 to Bax ratio at the top of crypts increased versus controls (+0.46 versus -0.85; P = 0.03). Bax density in the middle of crypts also decreased as minutes per week of exercise increased (P trend = 0.03).

CONCLUSIONS

A 12-month exercise intervention resulted in greater expression of proteins that promote apoptosis at the bottom of colon crypts in men and decreased expression of proteins that promote apoptosis at the middle and top of colon crypts in women. The difference in effect by gender and location of observed changes warrants further study.

Exercise and colon cancer: primary and secondary prevention

Many studies have demonstrated the effects of exercise on both primary and secondary prevention of colon cancer. Exercise appears to have a dose-response reduction in the rate of colon cancer. The mechanism by which exercise provides this benefit is not known, but increase in insulin-like growth factor-binding protein and reduction of prostaglandins appear to be the likely cause. Once a person develops colon cancer the benefits of exercise appear to continue both by increasing quality of life and reducing cancer-specific and overall mortality.

Exercise and biomarkers for cancer prevention studies

The International Agency for Research on Cancer estimates that 25% of cancer cases worldwide are caused by overweight or obesity and a sedentary lifestyle. These lifestyle patterns may increase cancer risk by several mechanisms including increased estrogens and testosterone, hyperinsulinemia and insulin resistance, increased inflammation, and depressed immune function. Several randomized clinical trials have shown that physical activity and diet interventions can change biomarkers of cancer risk. In a controlled physical activity trial, we found decreases in serum estrogen, testosterone, and insulin in overweight, sedentary postmenopausal women with a 1-y exercise program consisting of moderate-intensity aerobic exercise, 45 min/d, 5 d/wk. In another controlled trial in middle-aged to older persons, we found that a 1-y exercise intervention of 60 min/d, 6 d/wk, reduced colon crypt cell proliferation in men who adhered closely to the program. Only 1 trial, the Women's Health Initiative Dietary Modification Trial, has published results of a dietary intervention on breast cancer incidence and reported a statistically nonsignificant 9% reduction in invasive breast cancer incidence in postmenopausal women following a low-fat dietary pattern for 8-12 y. Other trials under way are testing effects of weight loss, physical activity, and dietary patterns on other cancer biomarkers. The NCI-funded Transdisciplinary Research on Energetics and Cancer centers are exploring novel research into mechanisms linking energy balance with cancer risk and prevention. The worldwide trends toward increasing overweight and obesity and decreasing physical activity may lead to an increased incidence of several cancers unless other means of risk reduction counteract these effects. Thus, adoption of lifestyle changes by individuals and populations may have a large impact on the future incidence of cancer.