Hepatoma Formation in ddY Mice with Chronic Schistosomiasis japonica

Three hundred and ninety‐five four‐week‐old SPF female ddY mice were each exposed to 5 or 6 cercariae of Schistosoma japonicum (Japanese strain) on their shaved abdomens and were maintained in a conditioned clean environment and fed on sterilized food and water. Fecal examinations at 8 to 10 weeks postinfection (PI) revealed 169 mice to be infected. More than half of them died within 30 weeks PI and 70 mice that survived to the 50th week PI were sacrificed. At autopsy, we could find no schistosome eggs in the liver or intestinal wall of 9 mice, and they were excluded. Out of 61 mice which showed S. japonicum eggs in their livers, 48 had single or multiple hepatoma, while no tumor was observed in the livers of the 60 control mice. The tumors were yellowish‐white in color with distinct boundaries and the centers of the tumors were depressed in some cases. The size of the tumors varied from 1 to 20 mm in diameter. Most of the tumors retained the normal trabecular pattern, but in some cases the trabeculae were thickened, having wide vascular spaces. The tumor cells were PAS‐negative and showed varieties of pleomorphism. The sizes of cells and nuclei varied greatly. These findings suggested some causal relationship between S. japonicum infection and the hepatoma formation in the host's liver. In the chronic course of Schistosomiasis japonica in the endemic areas, S. japonicum infection probably plays a role in hepatoma formation of patients.