Obesity is associated with improved survival in patients with organ-confined clear-cell kidney cancer

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 assessed whether different body mass index (BMI) levels at the time of surgery had an effect on long-term prognosis of RCC patients. Methods: We evaluated 1,338 clear-cell RCC patients with complete information about their BMI, who had undergone surgery for renal cell cancer at the University Hospitals in Hannover and Marburg between 1991 and 2005. The mean follow-up was 5.1 years. Results: Underweight, normal weight, pre-obesity, and obesity were diagnosed in 14 (1.0%), 444 (33.2%), 593 (44.3%), and 287 (21.4%) RCC patients, respectively. A lower BMI was significantly associated with higher age, tumor grade, and the rate of metastasis at diagnosis. Overweight patients had a significantly lower risk of cancer-related death; their median 5-year tumor-specific survival rate was 70.9% (pre-obese), 74.0% (obese grad I), and 85.6% (obese grad ≥II) as opposed to 63.8% for patients with a BMI below 25 (p < 0.001). Interestingly, subgroup analysis revealed that the positive association between overweight and survival was found in organ-confined RCC only. Conclusion: We identified overweight as an independent prognostic marker of improved cancer specific survival in patients with organ-confined but not advanced RCC. Basic research is required to resolve the dilemma of why, if a higher BMI predisposes to RCC, it concurrently prolongs survival after patients have undergone (partial) nephrectomy.