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The electron-microscopy investigation of osteogenic sarcomas of the osteoplastic type made it possible to identify 4 types of cells with a various ultrastructure. The cells of osteogenic sarcoma retain the ultrastructural specificity of skeletogenous cells and some features of tissue organization. This confirms once more the statement that osteogenic sarcoma is a derivative of the precursor of skeletogenous cells which underwent a tumour transformation.

An immunohistochemical analysis of nonproliferating epithelial structures was carried out in 10 samples of human breast dysplasia and in 4 samples of tissue surrounding mammary gland carcinoma. Monoclonal mouse antibodies against individual prekeratins of rat monolayer epithelial antibodies of clone C12 against rat prekeratin with the molecular mass 49 kilodalton and antibodies of clone E3 against rat prekeratin with the molecular mass 40 kilodalton-monoclonal antibodies against vimentin (clone 30), as well as polyclonal antibodies against smooth muscle myosin and against the basement membrane glycoprotein laminin were used. The lining epithelium of all glandular structures reacted only with C12 antibodies. Two variants of myoepithelial cells containing myosin were detected. Variant I contains myosin and vimentin and is localized in intralobular ducts. Variant 2 contains myosin and prekeratin, recognized by E3 antibodies and is found in extralobular ducts.

Electron microscopic study of osteogenic sarcomas has revealed association of the product of the reaction for alkaline phosphatase with membranous structures. The structural and function polymorphism of osteogenic sarcoma cells is also shown.

Immunomorphologic study of 29 breast cancer cases using monoclonal antibodies to proteins of intermediate filaments shown to differentiate the lining epithelium from myoepithelium in the non-proliferating epithelial structures of the mamma, has shown the cells in the majority of tumours (according to the International WHO Classification defined as infiltrating ductal, lobular, and tubular cancer forms) to contain prekeratin (PK) C12, specific for normal lining epithelium, but not for the myoepithelium. In cases of cancer with chondroid metaplasia (a malignant variant of the so-called "mixed tumour") the cells contained PK E3, vimentin and structural myosin, normally specific for myoepithelium. The cell heterogenicity in PK C12 content or its absence noted in the infiltrating cancers with predominance of a solid component can indicate a high degree of tumour anaplasia. It is concluded that usage of monoclonal antibodies to PK C12, invariably found in the cells of fibrotic invasion foci, can be a useful indicator for early diagnosis of infiltrative tumour growth.

Malignant melanoma operative specimens from 3 patients, containing a substantial proportion of melanin as well as the MeWo cell line also containing the pigment, gave rise to human melanoma strains transplanted to nude mice and rats. All the strains demonstrated a rapid decrease in melanin production compared to the original material. The pigment was detectable by electron microscopy alone.