Comparative pathology and ultrastructure of rodent sarcomas induced by the murine sarcoma virus (Moloney)

Murine sarcoma virus (M) of mouse origin induced non-regressing tumours in newborn BALB c mice, Osborn-Mendel rats and in newborn Syrian golden hamsters. Cell-free extracts obtained from these rat and hamster tumours were oncogenic in animals of the same species. With continued serial passage of the viruses in mice, rats or hamsters, there was a progressive increase in malignancy, manifested by a reduced survival time and a loss of characteristic morphology. The morphological features of the sarcomas induced in the mouse, rat and hamster with the initial virus passages indicated myoblastic entities. The mouse tumour cell is the most differentiated in the direction of a muscle cell and the hamster tumour the least differentiated. After successive cell-free passages in mice, rats and hamsters, the tumours were composed of undifferentiated mesenchymal cells, as revealed by light and electron microscopy. In view of this finding the neoplasm could be best classified as an undifferentiated sarcoma.