Background and aim:The transcriptional co-activator Yes-associated protein-1(YAP1)has been impli-cated as an oncogene and is overexpressed in different kinds of human cancers,especially hepatocellular carcinoma(HCC).However,the role of YAP1 has not been reported in residual/recurrent HCC after transarterial chemoembolization(TACE).Our aim is to determine whether YAP1 is overexpressed in the residual/recurrent HCC after TACE. Methods:A total of 105 tumor tissues from 71 patients including 30 cases of primary HCC without prior treatment,35 cases of residual/recurrent HCC post TACE,and 6 cases of hepatoblastoma were included in the immunohistochemical study.YAP1 immunoreactivity was blindly scored as 0,1+,2+or 3+in density and percentages of positive cells. Results:About 33.3％(10/30)of primary HCC without prior treatment showed 2+of YAP1 immunore-activity.While 82.8％(29/35)of residual/recurrent HCCs after TACE treatment displayed 2-3+of YAP1 immunoreactivity,which was significantly higher compared to primary HCC without prior treatment(P=0.0002).YAP1 immunoreactivity was moderately to strongly positive(2-3+)in 100％ of the hep-atoblastoma,particularly in the embryonal components(3+ in 100％ cases). Conclusions:YAP1 is significantly upregulated in the residual/recurrent HCCs post TACE treatment,suggesting that YAP1 may serve as a sensitive diagnostic marker and a treatment target for residual/recurrent HCC post TACE.