{'fraction_non_alphanumeric': 0.016118633139909737, 'fraction_numerical': 0.0, 'mean_word_length': 5.897777777777778, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Light and electron microscope studies of osteosarcomas induced in rats and hamsters by Harvey and Moloney sarcoma viruses.

Summary The histological and ultrastructural appearances of osteosarcoma induced in rats and hamsters by intraperitoneal inoculation of Moloney and Harvey murine sarcoma viruses are described. The osteosarcomas were multicentric, periosteal, and predominantly osteogenic in animals of both species. The tumors contained areas of osteolytic, chondrogenic, angiosarcomatous, histiocytic, and mesenchymal cell proliferation as satellite growths in the surrounding parenchyma. Invasion of the marrow space and adjacent skeletal muscle by the malignant osteoblasts, anaplastic sarcoma cells, and multinucleated giant cells was frequently observed. Ultrastructural details of the osteocytes, chondrocytes, osteoblasts, myoblasts, histiocytes, giant cells, and anaplastic or undifferentiated tumor cells seen in the osteosarcomas by light microscopy are described. Type C virus particles shown to be the causative agent of these tumors were present in different stages of development in all tissues and cells examined. They were also present in tissue culture cells derived from the primary osteosarcomas. Bernhard type H particles were observed in several osteosarcoma specimens. The significance of these particles remains to be determined. The induction of osteosarcomas by murine sarcoma virus in animals of more than one species adds further support for continuation of studies on possible viral etiology of osteosarcomas in man.