Objectives: Obesity increases the risk of developing renal cell carcinoma (RCC); however, it remains unclear whether obesity is associated with RCC aggressiveness and survival. We used data from a large cohort of patients treated surgically for clear cell RCC to evaluate the association of obesity with the pathologic features of tumor aggressiveness and cancer-specific outcomes. Methods: From 1988 to 2002, 970 patients underwent nephrectomy at Mayo Clinic Rochester for clear cell RCC and had body mass index (BMI) data available. To evaluate the association of BMI at surgery with the tumor pathologic features, we used the chi-square and Fisher's exact tests. We then analyzed the association of BMI with cancer-specific survival using Kaplan-Meier curves and Cox regression models. Results: Overweight (BMI 25 to less than 30 kg/m2) and obese (BMI 30 kg/m2 or more) patients were more likely to present with less-aggressive tumors compared with normal-weight patients (BMI less than 25 kg/m2). The 5-year cancer-specific survival rate was 62.3%, 76.9%, and 81.7% for the normal, overweight, and obese patients, respectively. The overweight (hazard ratio 0.64, 95% confidence interval 0.49 to 0.84) and obese (hazard ratio 0.48, 95% confidence interval 0.36 to 0.66) patients were at a reduced risk of RCC death compared with patients with a BMI in the normal range. The inverse association of BMI with survival was attenuated after adjustment for well-known pathologic predictors of tumor aggressiveness. Conclusions: BMI offers little additional prognostic information beyond the accepted prognostic features; however, the association of an increased BMI with a less-aggressive disease profile at presentation warrants further exploration.
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