Recent results of the German Thorotrast study--pathoanatomical changes in animal experiments and comparison to human thorotrastosis.

A survival experiment is described in which 1920 Wistar rats were used. These rats were injected intravenously with different quantities and different alpha-doses of Thorotrast. The following observations were made: The distribution of Thorotrast in the liver of the experimental animals is similar to that in human livers. Liver fibrosis and liver cirrhosis are rarely seen in experimental animals. The liver cell carcinomas, intrahepatic bile duct carcinomas and haemangiosarcomas that developed in the liver of the rats showed an identical biology and morphology with those seen in corresponding Thorotrast tumours in human patients. One particular tumour type that occurred in the liver of the rats probably represents a Kupffer cell sarcoma: the tumour cells show a positive peroxidase reaction and the metastases contained Thorotrast. Unlike human Thorotrast liver tumours, rat liver tumours include benign tumours such as liver cell adenomas and intrahepatic bile duct adenomas. The animals of the control group did not develop these benign liver tumours. The total frequency of the liver and spleen tumours in the trial groups receiving 230Th enriched Thorotrast was dependent on the dose given. The relationship between dose and effect was almost linear. The volume of the injected Thorotrast quantity, given a constant dose rate, seems to have only a slight influence on the number of tumours.