Obesity in Relation to Renal Cell Carcinoma Incidence and Survival in Three Prospective Studies.

To disentangle the "obesity paradox" in renal cell carcinoma (RCC), we examined associations of body mass index (BMI) and weight change with RCC risk and survival in the Health Professionals Follow-up Study (HPFS) and Nurses' Health Study (NHS) 1 and 2. We estimated cohort-specific and summary covariable-adjusted hazard ratios (HRs) and 95% confidence intervals (CIs) for RCC incidence, as well as RCC-specific survival among cases in the pooled HPFS and NHS data. Cumulative average BMI was associated with a higher risk of total RCC (summary HR 2.16, 95% CI 1.77-2.63 for BMI ≥30 vs 18-<25 kg/m2; p trend <0.001) and fatal RCC (HR 2.03, 95% CI 1.37-3.01; p trend <0.001). Prediagnosis BMI was not associated with RCC death. However, first postdiagnosis BMI (HR 0.51, 95% CI 0.29-0.89; p trend 0.006) and prediagnosis to postdiagnosis weight change (HR 0.52, 95% CI 0.29-0.91; p trend 0.001) were significantly inversely associated with RCC death. These results support obesity as a risk factor for total and fatal RCC. They undermine the obesity paradox by suggesting that weight loss around diagnosis, and not low BMI itself, is associated with worse prognosis. PATIENT SUMMARY: We studied obesity in kidney cancer and found that obesity is associated with getting and dying from the disease. Body mass index at diagnosis is not an ideal factor for predicting prognosis, as patients who have lost weight are likely to have more aggressive cancer.