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The osteosarcomas were subclassified into osteoblastic, fibroblastic, chondroblastic and telangiectatic types and examined by electron microscopy. Their immunohistochemical reactions were also studied. In an overall survey of the above types, fibroblast-like cells revealed poorly developed cytoplasmic organelles with rather short, branching rough endoplasmic reticulum, mixed with osteoblast-like cells that were hardly distinguishable from the former. They appeared to be an early stage of an osteoblastic cell lineage from the distribution and development of their cell organelles and highly positive vimentin activity. The tumor cells in malignant cartilage varied in appearance from chondroblast-like to osteoblast-like cells. All types of tumor cells expressed alkaline phosphatase activity to a significant degree. Immunohistochemical staining showed a mixture of procollagen type I-positive cells among the cells positive for both procollagen type II and S-100 protein in the malignant cartilage. Irrespective of any ultrastructural differences between these various tumor cell types, they all revealed a significant degree of ALPase activity unlike other types of bone tumors, suggesting that the tumor cells which constitute the various types of osteosarcoma are derived from a common precursor cell.

An ultrastructural survey of 11 human tumors passaged in N:NIH(S) (nu/nu) mice showed two instances of type C virus production. In one instance type C virus particles were observed in the endothelial murine stromal cell component of an embryonal carcinoma but not in the human tumor cells. In another instance type C virus particles were seen replicating in the chondroblastic human cells of a xenografted osteosarcoma. The type C virus produced in the human cells failed to transform NIH/3T3 cells, the C-127 rat cell line, or mink cells. Nucleic acid hybridization studies in which a human endogenous retroviral probe and a xenotropic murine leukemia virus envelope probe were used suggested that the retrovirus present in the human osteosarcoma cells is related to murine leukemia viruses. Intracisternal A-particles (IAP) were also detected in the human osteosarcoma cells. Their presence in the human cells was demonstrated by simultaneous visualization of IAP and human HLA determinants at the cell surface. The literature on type C virus infection of human cells and tumors grafted in nude mice is reviewed.

A classical osteogenic sarcoma of the breast is described and the results of light microscopy, including immunohistochemistry for epithelial and mesenchymal markers, and of electron microscopy are presented. No epithelial features were detected by any of the methods used, the tumour being considered a true osteogenic sarcoma. The tumour appears to have arisen de novo, and not from a pre-existing fibroadenoma.

The ultrastructural study of three malignant orbital tumors, only one of which was correctly diagnosed as embryonal rhabdomyosarcoma upon histologic examination, is reported. In all 3 cases electron microscopic investigation revealed the presence of rhabdomyoblasts. These are easily recognizable in one case in which the diagnosis was made on the basis of the optical microscopic study. The other two cases needed further tests to evince rhabdomyoblasts. The importance of an ultrastructural study for a histogenetic characterization of this kind of tumor is emphasized. As far as embryonal rhabdomyosarcomas are concerned the electron microscopic study is possible, and it gives useful results even when material fixed with routine histologic methods (formalin, Bouin's solution) are used.

Electron-microscopic studies in which Alcian blue was used to demonstrate proteoglycans (PG) revealed a predominance of largely undifferentiated tumor cells in two of the osteosarcomas examined; the extracellular matrix of these tumors had few PG-containing structures. Other osteosarcomas, where cells of the osteoblastic type prevailed, were found to possess PG granules on the cell surface and a rough PG network in the pericellular space. In a parosteal osteosarcoma, which contained strongly elongated fibroblast-like cells, PG formed a fine mesh both in the pericellular space and throughout the extracellular matrix. A correlation therefore exists between the ultrastructure of the PG component in the extracellular matrix of osteogenic sarcomas and the degree and direction of tumor cell differentiation.

Confronting cisternae of the endoplasmic reticulum recognized in tumor cells of 7 cases of osteosarcoma were presented. They were found in the mitotic cells as well as in the cytoplasms of interphase cells. The more the mitotic cells were observed in 1 micron-thick sections, the more frequently those membranous structures were encountered in the corresponding ultrathin sections. In the interphase cells, such structures were located around Golgi apparatus or close to the nucleus. Occasionally, they were composed of a pair of closely apposed cisternae of the nuclear membrane and the rough endoplasmic reticulum. These results seem to indicate that the nuclear envelope which is disrupted and reformed during mitosis in rapidly proliferating cells takes part in the formation of the confronting cisternae of the endoplasmic reticulum.

A case of osteosarcoma arising in the soft tissue of the larynx in an elderly man is presented with light and electron microscopic documentation. The patient developed chronic hoarseness and a recurring polypoid laryngeal tumor, causing acute airway obstruction. He was treated by total laryngectomy, but he died with multiple pulmonary metastases within three months of laryngectomy. This is the third (or possibly fourth) recorded case of osteosarcoma arising in the soft tissues of the larynx, and the previous cases were clinically and pathologically similar to this one. The prognosis of sarcoma of the larynx is poor but may be improved with early recognition and adequate surgical excision.