The loss of BAP1 protein expression predicts poor prognosis in patients with nonmetastatic clear cell renal cell carcinoma with inferior vena cava tumor thrombosis

Abstract Objectives Renal cell carcinoma (RCC) is characterized by a propensity for extension into the renal vein and inferior vena cava (IVC) and is associated with poor prognosis. BAP1 mutation, which occurs in about 15% of patients with clear cell RCC (ccRCC), also predicts poor prognosis. The aim of this study was to elucidate the association between BAP1 protein expression and clinicopathological outcomes in patients with nonmetastatic ccRCC with an IVC tumor thrombus (IVCTT). Material and methods Thirty-five patients with nonmetastatic ccRCC with an IVCTT who underwent radical nephrectomy and tumor thrombectomy at our institution from 1999 to 2010 were retrospectively evaluated. Immunohistochemical (IHC) analyses were performed for the expression of BAP1 protein, and the associations between the expression of BAP1 and clinical outcomes were assessed. Survival analyses were performed using the Kaplan-Meier method and log-rank test. Multivariate analyses of the associations between disease-free survival (DFS) and clinical variables including BAP1 protein expression, tumor size, Karnofsky performance status (KPS) score, and the extension level of the tumor thrombus were performed using a Cox proportional hazard model. Results The median follow-up time was 58.8 months (range: 2–130 months). The median age was 68 years (range: 37–80 years). The median size of the primary tumor was 9.6 cm (range: 3.0–15.0 cm). The IVCTT extended above and below the diaphragm in 10 (28.6%) and 25 (71.4%) patients, respectively. The KPS score was>80 in 23 patients (65.7%). BAP1 protein expression on IHC was positive in 24 cases (68.8%) and negative in 11 cases (31.2%). The median overall survival in cases with BAP1-negative and -positive tumor on IHC staining were 44.7 and 81.5 months, respectively ( P = 0.052). BAP1-negative tumor on IHC staining was associated with a significantly shorter DFS than BAP1-positive tumor (median DFS = 10.0 vs. 26.0 months, respectively; P = 0.011). Multivariate analysis showed that only BAP1-negative tumor on IHC staining was significantly associated with shorter DFS ( P = 0.004). Conclusions Patients whose tumors had loss of BAP1 protein expression were significantly associated with poor prognosis in patients with ccRCC with an IVCTT who underwent radical nephrectomy and tumor thrombectomy.