To determine the clonal evolution of hepatocellular carcinoma, the integrated hepatitis B virus DNA patterns of the main tumor, satellites and/or metastatic lesions were analyzed by Southern-blot hybridization in 28 hepatocellular carcinomas, including three HBsAg-seronegative cases. Unicentric or multicentric hepatocellular carcinoma was confirmed by histopathological criteria in 89% of the cases. Among 17 unicentric hepatocellular carcinomas, minor changes of the integration pattern--including partial loss or addition of the integration sites or both--were detected in the metastatic lesions in 29% of the cases. Furthermore, none of five cases with free-form hepatitis B virus DNA in the primary tumor had detectable free hepatitis B virus DNA in the metastatic lesions. These results suggest that the alteration of integrated hepatitis B virus DNA pattern during the course of tumor growth and metastasis may occur more often than previously perceived and that the switch-off of virus replication may be related to tumor metastatic potential. In eight cases with unilateral, multicentric hepatocellular carcinoma, two clones were detected in six cases, three were seen in another and four were seen in one. One case of note was a 9-yr-old boy with two histological types and two different integration patterns, one associated with vascular invasion and lung metastasis. Three patients with bilateral hepatocellular carcinoma were confirmed to have bicentric or tricentric hepatocellular carcinoma rather than intrahepatic dissemination and had survival rates similar to those in unicentric hepatocellular carcinoma. Three invasive HBsAg-seronegative hepatocellular carcinomas were found to have hepatitis B virus DNA integration and were of unicentric origin.(ABSTRACT TRUNCATED AT 250 WORDS)