751Investigation of the obesity paradox in kidney cancer: mystifying association or myth?

Abstract Background An “obesity paradox” has been reported in kidney cancer, whereby obesity is a risk factor, yet appears to be associated with better survival. To evaluate this paradox, we investigated the association between pre-diagnostic adiposity and renal cell carcinoma (RCC) incidence and mortality. Methods Using data from 363,521 men and women in the European Prospective Investigation into Cancer and Nutrition (EPIC), Cox regression models yielded confounder-adjusted hazard ratios (HRs) and 95% confidence intervals (CIs) for RCC incidence and mortality in relation to BMI modelled continuously and using restricted cubic splines. RCC-specific and all-cause mortality were evaluated among cases. Results During a mean follow-up of 14.9 years, 936 incident RCC cases were identified, 383 of whom died (278 due to RCC). Each 5 kg/m2 increment in BMI was associated with 27% and 46% higher RCC incidence and mortality (HRs=1.27, 95% CI 1.18-1.37 and 1.46, 95% CI 1.28-1.66, respectively). Comparing a BMI of 35 with 22 kg/m2, HRs for RCC incidence and mortality were 1.88 (95% CI 1.54-2.30) and 2.37 (95% CI 1.68-3.35), respectively. Among RCC cases, HRs per 5 kg/m2 increment in BMI were 1.22 (95% CI 1.07-1.41) for RCC-specific mortality and 1.18 (95% CI 1.04-1.34) for all-cause mortality. Similar, positive linear associations were evident for waist circumference and waist-to-hip ratio. Conclusions Obesity was associated with increased RCC incidence and mortality, and worse prognosis among cases. Key messages The kidney cancer-obesity paradox does not appear to be real. Higher adiposity is associated with an increased risk of incident and fatal RCC.