Malignant bone tumours induced by a local injection of colloidal radioactive 144Cerium in rats as a model for human osteosarcomas.

Lung metastases were observed in 80% to 85% of rats bearing advanced malignant bone tumours (osteogenic osteosarcomas and angiosarcomas). These tumours were induced in 2-month-old Sprague-Dawley rats by inoculation of a colloidal suspension of radioactive cerium (144Ce) into the hind leg, in close contact to the bones of the knee joint. Twenty-eight rats were killed or died spontaneously shortly after detection of palpable tumours at the site of injection: the incidence of lung metastases was 73.3% and 53.8%, respectively, for osteogenic sarcomas and angiosarcomas, showing that most lung metastases are present at the time of diagnosis of the primary tumour. Tumour-cell kinetic parameters were studied in 49 rats bearing tumours following intraperitoneal injection of [3H]thymidine. The labelling index (LI) of the primary tumours was significantly lower in advanced tumours (7.2% for osteosarcomas and 10.1% for angiosarcomas) than than in tumors examined at the time of detection (12.2% and 13.5%, respectively). Mitotic indices (MI) of all tumours were less than 1%. From the curve of the percentage of labelled mitoses (PLM) at different times after [3H]thymidine injection, Ts (6.5 h) and TG2 (1.75 h) were determined. TC and TG1 were also evaluated (18 h and 9.25 h, respectively). These results show that malignant bone tumours induced in rats with 144Ce may be a good model for human osteosarcomas and may be useful in studying the numerous problems in the therapy of malignant bone tumours in man.