LAUSR

554 Background: Partial nephrectomy is the standard surgical treatment for T1a renal cell carcinoma (RCC) and select T1b. Among these tumor classes, the tumor location can be divided into inner or outer. However, little attention has been paid to the mechanism of the pattern of RCC growth. In our body, there are two types of adipose tissue: white adipose tissue (WAT) and brown adipose tissue (BAT). WAT is important for energy storage and BAT is important for thermogenesis. BAT expresses uncoupling protein 1 (UCP-1), and mainly located in mediastinal, supraclavicular and perirenal tissues. But no studies have been done to investigate the relationship between RCC and BAT.In this study, we examined the association between adipose tissue, especially around kidney, and the growth pattern of RCC. Methods: We retrospectively reviewed computed tomography scans of 153 patients with stage 1 RCC who underwent radical or partial nephrectomy in our hospital between January 2013 and July 2016. We calculated the visceral/subcutaneous/perirenal fat volumes using SYNAPSE VINCENT. Of the 60 patients, the perirenal fat was immunohistochemically stained for leptin, adiponectin, COX-2 and UCP-1, and the association with outward tumor protrusion was evaluated. Results: Of the 153 cases, 88 had confirmed outward expansion (57.5%), 110 were classed as pT1a (52 and 58 with outer and inner expansion, respectively), 43 were classed as pT1b (36 and 7 with outer and inner expansion, respectively; P < 0.0001). Multivariate Cox model showed a trend toward significance in pT1b (vs. pT1a, OR 6.033, 95% CI = 2.409-15.108, P = 0.0001), perirenal fat percentage > 1.0 (vs. ≤ 1.0, OR 2.596, 95% CI = 1.205-5.591, P = 0.014). as independent predictors for outer protrusion. Immunohistochemical staining was positive for UCP-1 expression in 31 out of 41 outgrowth types (75.6%), and all 19 endogenous types (100%; P = 0.003). Conclusions: Renal cell carcinoma with thick perirenal fat correlates with an increased likelihood of developing outward tumor protrusion; therefore, fat distribution and UCP1 expression may affect the development of renal cell carcinoma.