Abstract
Osteosarcomata induced in rats by 32P injections had histological appearances resembling those in other experimental animals and in man. The fine structure of most of the component cells was like that generally ascribed to malignant cells and their structural organization was much more simplified than that of pre-osteoblasts undergoing hyperplasia in repair. They had relatively inconspicuous Golgi zones, limited endoplasmic reticulum and few mitochondria and it seemed unlikely that they played much part in matrix synthesis. Other cells more closely resembled osteoblasts and they were probably derived from the more primitive tumour cells rather than directly from the original bone cells. Presumably they secreted the matrix component of the hard tissue of the tumours. This matrix did not have any features labelling it neoplastic and its fine structure resembled that of fracture callus. Calcification patterns did not differ from the normal. Cells were included within the matrix and were analogous to osteocytes although some of the superficial ones had features of the undifferentiated cells.
The few multinucleated cells present resembled osteoclasts although most of them seemed to be non-functioning and lacked a brush border.
The thin-walled blood vessels traversing the tumours were lined by endothelial cells and not by tumour cells.