['As is known for many types of human cancers, the hepatocellular carcinoma (HCC) associated with chronic liver disease shows an obvious multistage process of tumor progression. Despite the demonstrated importance of cell-cycle regulators in tumor biology, there have only been a few studies of their role in multistep hepatocarcinogenesis. Recently, we reported that a high level of p27(Kip1) expression is evident from the very early stages of hepatocarcinogenesis.', 'In the present study, expression of p27(Kip1) and Jun activation domain binding protein-1 (Jab1), which is a key molecule involved in posttranslational regulation of p27(Kip1), was evaluated in surgically resected specimens of 8 dysplastic nodules (DNs), 16 early HCCs, and 126 classical HCCs.', 'Immunohistochemistry revealed no Jab1 expression in the majority of hepatocytes in noncancerous normal liver tissue and cases of chronic hepatitis or cirrhosis. In contrast, Jab1 was overexpressed in 50% (4/8) and 50% (8/16) of DNs and early HCCs, respectively, and the labeling index was increased in line with the degree of loss of differentiation in classical HCCs. Real-time quantitative reverse transcription polymerase chain reactions revealed the Jab1 mRNA levels in all tested early and well-differentiated HCCs to be increased compared with matched nontumorous liver specimens. The Spearman coefficient pointed to a high correlation between p27(Kip1) and Jab1 mRNA expression levels (P = 0.0014).'] Is jun activation domain binding protein 1 overexpressed from the very early stages of hepatocarcinogenesis?