Malignant bone tumours induced by a local injection of colloidal radioactive 144cerium in rats as a model for human osteosarcomasl

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Abstract
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 in tumours 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.