Abstract
INTRODUCTION AND OBJECTIVES: Obesity, as characterized by body mass index (BMI), is a risk factor for development of renal cell carcinoma (RCC), but paradoxically has been associated with decreased all-cause mortality (ACM) after surgery. However, BMI evaluates overall weight, which encompasses both adipose and muscle mass. While robust lean muscle mass appears to be protective, the independent impact of adipose burden on survival is unclear. Herein, we evaluate the impact of Fat Mass Index (FMI), a measure of total body fat mass, normalized by height on ACM, adjusting for lean muscle mass. METHODS: FMI was calculated from adipose tissue area at L3 measured on preoperative axial CT in 390 patients who underwent radical nephrectomy (RN) for localized RCC (2000-10). Patients were characterized as obese by FMI > 9 kg/m in males or >13 kg/m in females (class I III obesity). Skeletal muscle index was calculated, and sarcopenia was classified per sex-specific consensus definitions. CSS and OS were estimated by the Kaplan Meier method. Variables associated with cancer-specific (CSM) and ACM were summarized, adjusting for clinicopathologic variables and lean muscle mass. Median follow-up was 7.2 years. RESULTS: Median FMI was 9.4 kg/m. In total, 169 (44%) were obese, including 137/250 (55%) males and 32/131 (24%) females. 5-year CSS for obese and nonobese patients was 82% vs 81% (p1⁄40.17), respectively, while 5-year OS was 71% vs 68% (p 1⁄4 0.28). FMI was linearly associated with CSM (Fig). Adjusting for sarcopenia, age, ECOG, tumor size, stage, nuclear grade, and necrosis, no significant association between FMI and CSM (HR 0.99, p1⁄40.86) or ACM (HR 1.02, p1⁄40.42) was noted. Similarly, obesity by FMI criteria was not significantly associated with CSM (HR 1.15, p 1⁄4 0.57) or ACM (HR 1.06, p 1⁄4 0.72). However, patients with both sarcopenia and class I e III obesity demonstrated a trend towards increased CSM (HR 2.0, p 1⁄4 0.05) and ACM (HR 1.5, p 1⁄4 0.10). CONCLUSIONS: The obesity paradox might be related to the contribution of increasing lean muscle mass to overall weight. After nephrectomy, increasing adiposity is not independently associated with ACM or CSM after adjusting for lean muscle wasting, clinical and tumorspecific factors. Excess adipose burden may represent an additive insult to sarcopenia, and warrants further study. Source of Funding: none
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