Prevalence And Genetic Features Of Tmprss2-Erg Fusion In Chinese Patients With Prostate Cancer.

e17529 Background: Prostate cancer (PCa) is one of the most common malignancies, with rising incidence rate in China. The Cancer Genome Atlas (TCGA) revealed 53% of patients with PCa had ETS family gene fusions. The most frequent fusion type of ETS fusions is TMPRSS2-ERG, which may predicts resistance to taxane and androgen-deprivation therapies. The prevalence of TMPRSS2-ERG fusion in Chinese PCa patients evaluated by fluorescence in situ hybridization (FISH) or immunohistochemistry (IHC) varied from 7.5% to 78.0%. However, the sample sizes were small. In the present study, we investigated the prevalence and genetic features of TMPRSS2-ERG fusion by next generation sequencing (NGS) in a larger Chinese PCa cohort. Methods: Genomic profiling was performed through NGS from Chinese patients with PCa between January, 2017 and November, 2019. Formalin fixed paraffin-embedded (FFPE) tumor specimens or blood samples from participants were collected for NGS. IHC staining for PD-L1 expression was performed using PD-L1 IHC 22C3 pharmDx assay or Ventana PD-L1 SP263 assay. Data analyses were performed using SPSS and R 3.6.1. Results: A total of 526 Chinese PCa patients were included in this study. The median age was 70 (range, 29-90) years old. We observed 13.1% patients with a positive PD-L1 expression, 3.0% patients with MSI-H, and a median TMB of 4.0 muts/Mb (range: 0-72.9). TMPRSS2 fusions were detected in 47 (8.9%) PCa patients, and 6.8% of patients had TMPRSS2-ERG fusion, which is significantly lower than that of Caucasian patients. The PD-L1 expression pattern and TMB distribution of the TMPRSS2-ERG fusion-positive patients were similar with TMPRSS2-ERG fusion-negative patients, however no fusion-positive patients were identified as MSI-H. Among these 36 TMPRSS2-ERG fusion-positive patients, the most frequently somatic mutations were detected in TP53 (38.9%), AR (11.1%), ATM (11.1%), and PTEN (11.1%). 9 (22.2%) patients harbored somatic mutations in PI3K/ AKT/mTOR pathway that has been previously demonstrated to collaborate with ERG to promote prostate cancer progression. Conclusions: This study revealed the prevalence and genetic features of TMPRSS2-ERG fusion in Chinese PCa patients by NGS in the first time. Our results provide a better understanding of molecular features in Chinese TMPRSS2-ERG fusion-positive PCa patients.