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Physical activity may prevent pancreatic cancer by regulating body weight and decreasing insulin resistance, DNA damage, and chronic inflammation. Previous meta-analyses found inconsistent evidence for a protective effect of physical activity on pancreatic cancer but those studies did not investigate whether the association between physical activity and pancreatic cancer varies by smoking status, body mass index (BMI), or level of consistency of physical activity over time. To address these issues, we conducted an updated meta-analysis following the PRISMA guidelines among 30 distinct studies with a total of 10,501 pancreatic cancer cases. Random effects meta-analysis of cohort studies revealed a weak, statistically significant reduction in pancreatic cancer risk for high versus low levels of physical activity (relative risk (RR) 0.93, 95 % confidence interval (CI) 0.88-0.98). By comparison, case-control studies yielded a stronger, statistically significant risk reduction (RR 0.78, 95 % CI 0.66-0.94; p-difference by study design = 0.07). When focusing on cohort studies, physical activity summary risk estimates appeared to be more pronounced for consistent physical activity over time (RR 0.86, 95 % CI 0.76-0.97) than for recent past physical activity (RR 0.95, 95 % CI 0.90-1.01) or distant past physical activity (RR 0.95, 95 % CI 0.79-1.15, p-difference by timing in life of physical activity = 0.36). Physical activity summary risk estimates did not differ by smoking status or BMI. In conclusion, physical activity is not strongly associated with pancreatic cancer risk, and the relation is not modified by smoking status or BMI level. While overall findings were weak, we did find some suggestion of potential pancreatic cancer risk reduction with consistent physical activity over time.

Background: Despite the existence of numerous biologic pathways potentially linking increased physical activity to decreased risk of hematologic cancers, the associations between physical activity and subtype-specific hematologic cancers have not been comprehensively quantified. Methods: We conducted a systematic review and meta-analysis of physical activity in relation to subtype-specific hematologic cancers. We summarized the data from 23 eligible studies (15 cohort and eight case–control studies) and estimated summary relative risks (RR) and 95% confidence intervals (CI) using random-effects models. Results: When comparing high versus low physical activity levels, the RR for non-Hodgkin lymphoma was 0.91 (95% CI, 0.82–1.00), for Hodgkin lymphoma it was 0.86 (95% CI, 0.58–1.26), for leukemia it was 0.97 (95% CI, 0.84–1.13), and for multiple myeloma it was 0.86 (95% CI, 0.68–1.09). When focusing on subtypes of non-Hodgkin lymphoma, the RR for diffuse large B-cell lymphoma was 0.95 (95% CI, 0.80–1.14) and for follicular lymphoma it was 1.01 (95% CI, 0.83–1.22). In an exploratory analysis combining all hematologic cancers, high versus low physical activity levels yielded a statistically significant RR of 0.93 (95% CI, 0.88–0.99). Conclusions: Physical activity showed statistically nonsignificant associations with risks of non-Hodgkin lymphoma, Hodgkin lymphoma, multiple myeloma, and leukemia. These findings may not represent a true lack of associations given the variation in high versus low physical activity definitions, the quality of physical activity assessments, and the variability in hematologic cancer classification schemes in individual studies. Impact: Physical activity is unrelated to risks of subtype-specific hematologic cancers. Cancer Epidemiol Biomarkers Prev; 23(5); 833–46. ©2014 AACR.

Background: Physical activity may protect against bladder cancer through several biologic pathways, such as enhanced immune function and decreased chronic inflammation. Physical activity may also indirectly prevent bladder cancer by reducing obesity. A sizeable number of epidemiologic studies have examined the association between physical activity and bladder cancer, but the available evidence has not yet been formally summarised using meta-analysis. Methods: We performed a systematic literature review and meta-analysis of English-language studies published from January 1975 through November 2013. We followed the PRISMA guidelines and used a random effects model to estimate the summary risk estimates for the association between physical activity and bladder cancer. Results: A total of 15 studies with 5 402 369 subjects and 27 784 bladder cancer cases were included. High vs low levels of physical activity were related to decreased bladder cancer risk (summary relative risk (RR)=0.85, 95% confidence interval (CI)=0.74–0.98; I2=83% P-value for heterogeneity across all studies

Physical activity is related to decreased endometrial cancer risk. However, a comprehensive investigation of activity domains, intensities, time periods in life, and potential interaction with body mass index is unavailable. We performed a meta-analysis of physical activity and endometrial cancer studies published through October 2014. We identified 33 eligible studies comprising 19,558 endometrial cancer cases. High versus low physical activity was related to reduced endometrial cancer risk [relative risk (RR) = 0.80; 95 % confidence interval (CI) 0.75–0.85]. The corresponding RRs for recreational activity, occupational activity, household activity, and walking were 0.84 (95 % CI 0.78–0.91), 0.81 (95 % CI 0.75–0.87), 0.70 (95 % CI 0.47–1.02), and 0.82 (95 % CI 0.69–0.97), respectively (\(P_{difference} = 0.88\)). Walking/biking for transportation, walking for recreation, and walking without specification revealed summary RRs of 0.70 (95 % CI 0.58–0.85), 0.94 (95 % CI 0.76–1.17), and 0.88 (95 % CI 0.52–1.50), respectively (\(P_{difference} = 0.13\)). Inverse associations were noted for light (RR 0.65; 95 % CI 0.49–0.86), moderate to vigorous (RR 0.83; 95 % CI 0.71–0.96), and vigorous activity (RR 0.80; 95 % CI 0.72–0.90; \(P_{difference} = 0.35\)). A statistically significant inverse relation was found for postmenopausal (RR 0.81; 95 % CI 0.67–0.97), but not premenopausal women (RR 0.74; 95 % CI 0.49–1.13; \(P_{difference} = 0.78\)). Physical activity performed during childhood/adolescence, young adulthood/midlife, and older age yielded RRs of 0.94 (95 % CI 0.82–1.08), 0.77 (95 % CI 0.58–1.01), and 0.69 (95 % CI 0.37–1.28), respectively (\(P_{difference} = 0. 5 1\)). An inverse relation was evident in overweight/obese (RR 0.69; 95 % CI 0.52–0.91), but not normal weight women (RR 0.97; 95 % CI 0.84–1.13; \(P_{difference} = 0.07\)). In conclusion, recreational physical activity, occupational physical activity, and walking/biking for transportation are related to decreased endometrial cancer risk. Inverse associations are evident for physical activity of light, moderate to vigorous, and vigorous intensities. The inverse relation with physical activity is limited to women who are overweight or obese.

Physical activity may decrease gastroesophageal cancer risk through a reduction of oxidative stress and decreased chronic inflammation, yet few epidemiologic studies have been able to report a clear inverse association between physical activity and gastroesophageal cancer. Because no meta-analysis has investigated the relation of physical activity to gastroesophageal cancer, we conducted a comprehensive systematic review and meta-analysis according to the PRISMA guidelines based on 24 studies with a total of 15,745 cases. When we compared high versus low physical activity levels and summarized associations according to anatomic site and tumor histology, risk reductions were evident for esophageal adenocarcinoma [relative risk (RR) = 0.79, 95 % confidence interval (CI) = 0.66–0.94], gastric cardia adenocarcinoma (RR = 0.83, 95 % CI = 0.69–0.99) and gastric non-cardia adenocarcinoma (RR = 0.72, 95 % CI = 0.62–0.84). The risk reduction for esophageal squamous cell carcinoma (RR = 0.94, 95 % CI = 0.41–2.16) became statistically significant (RR = 0.66, 95 % CI = 0.46–0.96) after excluding an influential study. The test for heterogeneity by gastroesophageal cancer subtype was statistically non-significant (p-difference = 0.71). The RR of total gastroesophageal cancer for high versus low physical activity was 0.82 (95 % CI = 0.74–0.90). A dose–response analysis of frequency of physical activity and total gastroesophageal cancer risk revealed that the greatest risk reduction was achieved among those engaging in moderate to vigorous physical activity five times per week (RR = 0.67, 95 % CI = 0.58–0.79). Our results provide support for an inverse relation of physical activity, in particular exercise frequency, to gastroesophageal cancer risk.

Thyroid cancer incidence has been increasing more rapidly over time than the occurrence of cancers of other sites, and interest in potential adverse relations of diabetes and lack of physical activity to thyroid cancer risk is accumulating. We conducted a systematic review and meta-analysis of published epidemiologic studies on the relations of physical activity and diabetes to thyroid cancer according to the Meta-analysis of Observational Studies in Epidemiology guidelines. Published studies were identified through a search in MEDLINE and EMBASE. Random-effects models were used to summarize thyroid cancer risk estimates comparing high versus low levels of physical activity, and separately, comparing individuals with diabetes versus those without diabetes. Meta-regression analyses were performed to evaluate potential effect modification by study design and thyroid cancer risk factors. Information was extracted from seven studies of physical activity and thyroid cancer and from six studies of diabetes and thyroid cancer. The number of individuals from studies on physical activity was 939,305 (yielding 2,250 incident thyroid cancer cases) and from studies on diabetes it was 960,840 (yielding 1,230 cases). The summary relative risk (RR) estimate from cohort and case–control studies combined indicated no association between physical activity and thyroid cancer (summary RR 1.06, 95 % confidence interval (CI) 0.79–1.42). Subgroup-analyses revealed a significant positive association between physical activity and thyroid cancer in cohort studies (summary RR 1.28; 95 % CI 1.01–1.63), whereas the relation was suggestively inverse in case–control studies (summary RR 0.70; 95 % CI 0.48–1.03; p for heterogeneity = 0.005). Individuals with diabetes showed a borderline statistically significant increased risk of thyroid cancer compared with those without diabetes (summary RR 1.17; 95 % CI 0.99–1.39). The relations of physical activity and diabetes to thyroid cancer were not modified by sex, number of adjustment factors, and adjustments for adiposity, smoking, and study quality. In this comprehensive systematic review and meta-analysis, no significant association between physical activity and thyroid cancer was found. Diabetes showed a suggestive positive relation with risk of thyroid cancer.

Background: Increased body mass index (BMI) is an established colorectal cancer risk factor. High waist circumference or waist-hip-ratio (WHR) may better reflect an abnormal metabolic state and be more predictive of colorectal cancer risk than BMI. Methods: We examined BMI, waist circumference, WHR, and hip circumference in relation to colorectal cancer risk among 203,177 participants followed for 10 years. We derived standardized colorectal cancer risk estimates for each anthropometric parameter and compared predictive characteristics (Harrell's C-index). In women, we examined whether hormone replacement therapy (HRT) use modified the associations between anthropometric measures and colorectal cancer. Results: We ascertained 2,869 colorectal cancers. In men, increased colon cancer risks were associated with BMI [HR per SD, 1.14; 95% confidence interval (CI), 1.08–1.20], waist circumference (HR per SD, 1.17; 95% CI, 1.08–1.27), and WHR (HR per SD, 1.09; 95% CI, 1.04–1.14). In women, anthropometric variables were unrelated to colon cancer. For men and women, anthropometric variables were unrelated to rectal cancer. Compared with BMI, waist circumference and WHR did not materially influence colon cancer prediction models [C-index changes: −0.0041 and 0.0046 (men); 0.0004 and 0.0005 (women)]. In current HRT users, colon cancer was inversely or suggestively inversely associated with waist circumference (HR per SD, 0.78; 95% CI, 0.63–0.97) and WHR (HR per SD, 0.88; 95% CI, 0.76–1.01), but positively related to hip circumference (HR per SD, 1.39; 95% CI, 1.13–1.71). Conclusion: BMI, waist circumference, and WHR show comparable positive associations with colon cancer in men. Associations between anthropometric measures and colon cancer are weak or null in women, but there is some evidence for effect modification by HRT. Impact: These findings may improve our understanding of the relation of adiposity to colorectal cancer. Cancer Epidemiol Biomarkers Prev; 22(8); 1383–94. ©2013 AACR.