[The morphogenesis and histogenesis of an experimental malignant fibrous histiocytoma].

Light and electron microscopy, histochemistry, histoautoradiography and vital staining were used to assess changes occurring in subcutaneous connective tissue surrounding a DMBA-containing pill in rats, samples being obtained at 2-week intervals until malignant fibrous histiocytoma became apparent. Initial tumor lesions developing against the background of alterative-inflammatory and reparative changes included apparently atypical pleomorphic cells showing cytologic signs of malignant transformation which remained virtually unchanged in developed sarcoma. The study, therefore, failed to identify the stage of "presarcoma". A complex of morphologic and functional characteristics of the atypical cells revealed their fibroblastic nature. Progression of tumor was associated with appearance of cells of histiocytic pattern (as evidenced by high activity of acid phosphatase and non-specific esterases, thin villus-like outgrowths of cellular membrane and well-developed Golgi complex) which pointed to pronounced structural and functional variability of poorly-differentiated neoplastic fibroblasts. Tumor revealed xanthomatous and multinuclear giant cells, too. Malignant fibrous histiocytoma is, therefore, poorly-differentiated polymorphocellular sarcoma of fibroblastic origin.