A virus antigen (HBsAg) indicates metastases of human carcinoma cells in the nude mouse.

The human hepatoma cell line PLC/PRF/5 produces tumours and lung metastases in nude athymic mice. Here we describe how detection of hepatitis B virus surface antigen, a marker of these cells, as led to identification of pancreatic and muscle metastases. The antigen was shown in the tissues, and antigen-producing PLC/PRF/5 cells were isolated from them. The number of cells detectable by this method is between 5 and 10 million. The principle used here may be adaptable be useful in studying micrometastasis formation in other systems.