Abstract 961: Joint associations of physical activity and body mass index and the risk of excess body fatness-related cancer
Authors: Maliniak Maret L. , Gapstur Susan M. , McCullough Lauren E. , Rees-Punia Erika , Gaudet Mia M. , Um Caroline Y. , Guinter Mark A. , Fallon Elizabeth A. , Patel Alpa V. 
Published: August 2019

Abstract
Background: Consistent evidence has linked excess body fatness (EBF), typically measured in large epidemiologic studies using body mass index (BMI), with a higher risk of 13 types of cancer. Whether physical activity mitigates any of the excess risk associated with EBF is unclear—as few studies have examined the joint association between BMI and physical activity.
Methods: We examined the joint association of BMI and physical activity on the risk of 12 of the 13 EBF-related cancers (excluding meningioma and including esophagus [adenocarcinoma], gastric cardia, colon and rectum, liver, gallbladder, pancreas, postmenopausal breast, corpus uteri, ovary, kidney [renal cell], thyroid, and multiple myeloma) among 70,658 men and 72,209 postmenopausal women (median age: 63 years) without a history of cancer at study entry in the Cancer Prevention Study II Nutrition Cohort (1992-2013). Multivariable Cox proportional hazards models were used to calculate hazard ratios (HR) and 95% confidence intervals (CI) for the individual and joint associations between BMI (kg/m2) and recreational physical activity (MET-hours/week) at study entry and first cancer incidence.
Results: Between 1992-2013, 3,860 men and 9,001 women were diagnosed with an EBF-related cancer. Compared to normal weight (BMI 18.5-&lt;25 kg/m2), overweight (25-&lt;30 kg/m2) was associated with a modest increased risk of EBF-related cancer (men: HR 1.12; 95% CI: 1.04, 1.21; women: HR 1.13; 95% CI: 1.08, 1.19) and obesity (≥30 kg/m2) with a stronger risk (men: HR 1.48; 95% CI: 1.34, 1.63; women: HR 1.48; 95% CI: 1.40, 1.57). Higher levels of physical activity (&gt;15 vs. &gt;0-&lt;7.5 MET-hrs/wk) were associated with a lower risk for EBF-related cancer among women (HR: 0.90; 95% CI: 0.85-0.95) but less so among men (HR: 0.96; 95% CI: 0.88, 1.04). Among women, there was no evidence of interaction between physical activity and BMI for the risk of EBF-related cancer (P-interaction=0.59); however, there was suggestive evidence that the excess risk associated with overweight was modestly mitigated by the highest level of physical activity (HR: 1.00; 95% CI: 0.91, 1.10). Among men, there was some evidence of an interaction between BMI and physical activity on risk (P-interaction=0.06) with the higher risk associated with overweight limited to those who were inactive (HR: 1.27; 95% CI: 1.08, 1.49). However, risk was higher for obese men irrespective of physical activity level.
Conclusion: Our results suggest that higher levels of recreational physical activity may offset a small amount of the increased risk of EBF-related cancer among overweight men and women. However, physical activity does not appear to mitigate the strong effect of obesity (BMI ≥30 kg/m2) on risk of EBF-related cancers, thus reinforcing the importance of maintaining a healthy body weight even if physically active.
Citation Format: Maret L. Maliniak, Susan M. Gapstur, Lauren E. McCullough, Erika Rees-Punia, Mia M. Gaudet, Caroline Y. Um, Mark A. Guinter, Elizabeth A. Fallon, Alpa V. Patel. Joint associations of physical activity and body mass index and the risk of excess body fatness-related cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 961.