Comprehensive genetic characterization of TFE3-positive renal cell carcinoma.

Abstract

635 Background: MiT family translocation renal cell carcinoma (RCC) is very rare variant which has translocation of Xp11.2/TFE3 gene or t(6;11)/TFEB gene. Xp11.2 translocation RCC is predominantly reported in younger age and has aggressive features. However, its pathophysiology or genetic characteristics are rarely understood. The aim of the study is to describe the comprehensive genetic characteristics of TFE3-positive RCC diagnosed by immunohistochemistry. Methods: We identified patients who were clinically diagnosed as Xp11.2 translocation RCC by immunostaining positive of TFE3 from two tertiary referral hospitals. Among them, a total of 19 patients whose fresh frozen tissue and normal DNA were achieved were included in the analysis. Whole exome sequencing (WES) was performed to evaluate somatic mutations and copy-number variation (CNV). We also performed RNAseq on the TFE3-positive RCC, 7 clear cell RCC, and 4 normal kidney tissue for comparison. Fusion partners were identified and clustering analysis was done by RNAseq. Results: Mutational landscape of TFE3-positive RCC is unique by low somatic mutation rate and very rare COSMIC variants. High prevalence of CNV with loss of 3p, 6q, 9, gain of 5, 7, and 12 were most frequent. We identified NONO, RBM10, SFPQ, ASPSCR1 and PRCC as fusion partner as previously described. We could not find TFE3 fusion in 6 out of 19 patients by RNAseq, and they were older and had more mutations than the others. They were also genetically clustered with clear cell RCC. Oxidative reducatase pathway was upregulated and immune response and cell adhesion were downregulated by gene ontology results from heatmap clusters. These may promote metastasis, resistant to immunity and cell survival in poorer condition which could be potential mechanism of Xp11.2 translocation RCC aggressiveness. Conclusions: TFE3-positive RCC showed distinctive mutation pattern with low somatic mutation and rare common driver gene. One-third clinically diagnosed Xp11.2 translocation RCC (6/19) did not have real gene fusion even in TFE3 overexpression. They were older and had more somatic mutations than the others. Furthermore, they were clustered with clear cell RCC.