The impact of BMI on outcomes of patients with metastatic renal cell carcinoma treated with targeted therapy: An external validation data set and analysis of underlying biology from The Cancer Genome Atlas.

Abstract

405 Background: Obesity is a risk factor for renal cell carcinoma (RCC) and a poor prognostic factor across many tumor types. However, reports have suggested that RCC developing in an obesogenic environment may be more indolent. We recently reported on the favorable impact of body mass index (BMI) on survival in the International mRCC Database Consortium (IMDC). The current work aims to externally validate this finding and characterize the underlying biology. Methods: We conducted an analysis of 4,657 metastatic RCC (mRCC) patients (pts) treated on phase II-III clinical trials sponsored by Pfizer from 2003-2013. We assessed the impact of BMI on overall survival (OS), progression-free survival (PFS) and overall response rate (ORR). Additionally, we analysed metastatic pts from the clear cell RCC (ccRCC) cohort of TCGA dataset to correlate the expression of Fatty Acid Synthase (FASN) with BMI and OS. Results: At targeted therapy (TT) initiation, 1,829 (39%) pts were normal or underweight (BMI <25 kg/m2) and 2,828 (61%) were overweight or obese (BMI ≥25 kg/m2). Overall, the high BMI group had a longer median OS (23.4 months) than the low BMI group (14.5 months) (hazard ratio (HR) = 0.830, p= 0.0008, 95% CI 0.743-0.925) after adjusting for the IMDC prognostic risk group and other risks factors. In addition, pts with high BMI had improved PFS (HR=0.821, 95% CI 0.746-0.903, p<0.0001) and ORR (odds ratio =1.527, 95% CI 1.258-1.855, p<0.001). These results remain valid when stratified by line of therapy. When stratified by histological subtype, the favorable outcome associated with high BMI was only observed in ccRCC. Toxicity patterns did not differ between BMI groups. In the the Cancer Genome Atlas (TCGA) dataset (n=61), there was a trend towards improved OS in the high BMI group (p=0.07). FASN gene expression inversely correlated with both OS (p=0.002) and BMI (p=0.034). Conclusions: In an external cohort,we validate BMI as an independent prognostic factor for improved survival in mRCC. Given that this finding was observed in ccRCC only, we hypothesize that lipid metabolism may be modulated by the fat laden tumors cells. FASN staining in the IMDC cohort is ongoing to better investigate the obesity paradox in mRCC.