Objective To analyze the expression level of YEATS2 in hepatocellular carcinoma(HCC)about its clinical prognosis and therapeutic value based on biological information from the cancer genome atlas(TCGA)and human protein atlas(HPA)databases.Methods The mRNA expression data and clinical information of HCC were downloaded from the TCGA database,the expression of YEATS2 between HCC tissues and normal tissues was analyzed by using the R software,and the protein expression differences were preliminary verified by the HPA database.The expression differences of YEATS2 between various clinical features of HCC were compared,and their effects on the survival of HCC patients by Kaplan-Meier method and COX regression analysis were then evaluated.Receiver operating characteristic(ROC)curves were plotted to evaluate their diagnostic values.The biological functions of YEATS2 in HCC were analyzed using gene ontology(GO)and Kyoto encyclopedia of genes and genomes(KEGG)enrichment analysis.The relationship between YEATS2 expression and tumor microenvironment(TME)was analyzed by the"ESTIMATE"algorithm,and its relationship with tumor-infiltrating immune cells(TIICs)was assessed by CIBERSORT.Analysis of YEATS2 expression levels to immune checkpoints and drug sensitivity was performed using the R package.Results The expression of YEATS2 was increased in HCC tissues(P=4.96e-21),and its expression level was correlated with age,clinical stage,pathological grade and T stage(all P＜0.05).Overall survival(OS)(P＜0.001)and progression-free survival(FPS)(P=0.016)were decreased in HCC patients with high expression of YEATS2,COX regression results showed that the expression level ofYEATS2 was associated with poor prognosis in HCC patients(OS:HR=2.167,95％CI:1.441～3.261,P=2.06e-04),and it was an independent risk factor for predicting poor prognosis in HCC patients(OS:HR=1.891,95％CI:1.243～2.877,P=0.003).The ROC curve suggested the AUCs for 1,3 and 5 years were 0.677,0.622 and 0.612,respectively,indicating good predictive ability.The TCGA database screened a total of 6 764 differential genes in the YEATS2 high and low expression groups,of which 4 094 genes were up-regulated and 2 670 genes were down-regulated in the YEATS2 high expression group.The results of GO and KEGG enrichment analyses showed that the differentially differentiated genes in the YEATS2 high expression group were mainly enriched in immunoregulation,and cell cycle regulation drug resistance pathway.The results of the TME score showed that the YEATS2 high expression group caused a decrease in immunity score(P＜0.01).The correlation between YEATS2 and TIICs showed that YEATS2 expression was positively correlated with the level of M0-type macrophage infiltration levels(r=0.48,P＜0.001)and 23 immune checkpoint genes(r=0.20～0.46,all P＜0.05),and was negatively correlated with the CD8+T-cells,plasma cells and monocyte(r=-0.26,-0.29,-0.30,P=0.021,0.011,0.008).Drug sensitivity analysis showed that the half maximal inhibitory concentration(IC50)of cabozantinib,lincitinib,doxorubicin,and cyclobenzaprine in patients with high expression of YEATS2 was higher than those in patients with low expression(all P＜0.01).Conclusion YEATS2 was highly expressed in HCC,and the expression level was associated with poor prognosis in HCC patients.YEATS2 can be used as a biomarker for the clinical early diagnosis,prognosis and immunotherapy of HCC,which may provide new ideas for clinical diagnosis and treatment.