Expression of insulin-like growth factor II, alpha-fetoprotein and hepatitis B virus transcripts in human primary liver cancer. Insulin-like growth factor II is a fetal growth factor structurally and functionally related to insulin and insulin-like growth factor I. Its mRNA expression is developmentally regulated in human liver, the reexpression of insulin-like growth factor II fetal transcripts being often observed in primary liver cancer. Insulin-like growth factor II and alpha-fetoprotein mRNAs were studied in 16 human primary liver cancers, most of which were highly differentiated. Hepatitis B virus transcripts were also analyzed in the tumors from hepatitis B virus chronic carriers. alpha-Fetoprotein mRNA was detected in only four tumors and in one nontumorous cirrhotic tissue; all these samples also displayed insulin-like growth factor II fetal transcripts. Furthermore, fetal insulin-like growth factor II mRNAs were observed in five tumors and six nontumorous cirrhotic areas not expressing alpha-fetoprotein mRNA. The presence of hepatitis B virus RNA was only observed in tissues not expressing alpha-fetoprotein or fetal insulin-like growth factor II mRNA. In conclusion, fetal insulin-like growth factor II transcripts are more frequently observed than alpha-fetoprotein mRNA in highly differentiated liver cancers and in surrounding cirrhotic areas. The reexpression of fetal insulin-like growth factor II transcripts might then be a marker of early steps of liver cell transformation. 