Hepatocellular carcinoma (HCC) associated with chronic liver disease evolves from precancerous lesions and early HCC to a progressed form. Nodule-in-nodule-type HCC (progressed HCC within early HCC) represents the transition from early to progressed HCC and, therefore, is useful in molecular genetic analysis of HCC progression during multistage carcinogenesis. We compared expression profiles among 7 early components and 7 progressed components of nodule-in-nodule-type HCCs and their corresponding noncancerous liver tissues with oligonucleotide array. Of the approximately 12,600 genes that were analyzed, a set of 95 genes provided a molecular signature that distinguished between early HCC components and their noncancerous liver tissues, and a set of 92 genes distinguished between progressed and early HCC components. Of these genes, the most abundantly up-regulated gene in early HCC components (P <.001) was heat-shock protein 70 (HSP70). Real-time quantitative reverse transcription polymerase chain reaction (RT-PCR) confirmed this finding. Further immunohistochemical examination of HSP70 revealed its significant overexpression in early HCC compared with precancerous lesions (P <.001) and in progressed HCC compared with early HCC (P <.001). In conclusion, molecular signatures were clearly different in noncancerous liver tissue as compared with the early and progressed components of nodule-in-nodule-type HCC. Moreover, HSP70 could be a sensitive marker for the differential diagnosis of early HCC from precancerous lesion or noncancerous liver, a difficult distinction for pathologists due to very well differentiated histology with little atypia in early HCC.