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The microscopic morphology, histochemistry and electron microscopy of a non-ossifying fibroma of the upper metaphysis of the femur in a sixteen-year-old girl, is presented.

Two cases of malignant mesodermic tumours of the human mammary gland with osteogenic and chondrogenic structures were analysed by optical and electronic microscopical means. One of them was associated with an adenocarcinoma of the gland. The histological pattern was similar to that of those cases previously examined under the optical microscope in the mammary gland and in extraskeletal osteogenic sarcomas of soft tissues. When investigated under the electron microscope, the chondroblasts possessed a highly developed RER in active synthesis with an amorphous material which contributed to the building up of the ground substance matrix of the tumorous cartilage. Osteoid fields with scattered osteoblasts appear throughout the tumorous stroma and were associated with calcium deposits. They were continuous with fibroblasts and mesenchymal undifferentiated cells of a very immature character. Giant cells of osteoclastic type were included within the mononucleated mesenchymal cells mimicking bone osteoclastoma. The presence of all these cell types suggests the existence of a common malignant origin, the stem cell being differentiated into epithelial carcinomatous and mesenchymal sarcomatous chondral and osteogenic tissues.

A new approach, employing histochemical and electron-microscopic techniques was used in an attempt to obtain a more complete knowledge of estrogen-induced kidney tumor in the golden hamster (G.H.). Three estrogen derivatives, diethylstilbestrol (DES), diethylstilbestrol monoglucoronide (DESGA), and dimethyl ether (DESDME), were used on non-castrated male hamsters. DES had the highest incidence of tumor induction ( 69% of the animals) which is associated with other tumors (epididymal and hepatic adenomas); DESDME induced tumors in 31% , and non-neoplastic changes could be observed in the DESGA-intoxicated group. Histologically, three main types of structures were seen which might be present in the same tumor: solid-blastemal, more tubular-epithelial and papillary-cystic areas. These kidneys also had a pluricentric tubular dysplasia and an interstitial cell hyperplasia. A histochemical study of the embryonic metanephron and the interstitial cells of newborn G.H. kidney, when compared to the DES-induced kidney tumor and the dysplastic pretumoral foci, showed marked similarities between the enzymes present. The comparative ultrastructural analysis of the embryonic developing kidney and the tumor itself yields further evidence of an interstitial origin of the neoplasia, which has a poorly differentiated and ciliated cell structure. The estrogen-induced G.H. kidney tumor may well begin in the interstitial cells of the residual metanephric tissue in the kidney stroma.

The structure and the origin of the interstitial cells in the kidney of the golden Hamster during its embryonic development was studied. For this purpose kidneys from 11, 13, 15 and 17 day-old embryos were used. The histochemical observations as well as the electron microscopy demonstrated that the interstitial cells have a metanephric origin and are embryonically similar to the cellular elements that differentiate the primordial renal vesicles and later organise the epithelial portion of the nephrons. These cells seem to take part in the formation of the basal membranes during tubular genesis.