Morphological and immunohistochemical support for the interstitial cell origin of oestrogen-induced kidney tumours in the Syrian golden hamster.

The oestrogen-induced kidney tumour of the Syrian golden hamster has been extensively used not only as a model for renal carcinogenesis, but also for hormonal carcinogenetic studies. In spite of all the different approaches, its histogenesis remains unresolved. The two classical hypotheses are an epithelial origin (in the proximal convoluted tubules) or a mesenchymal-blastemal origin (in the interstitial cells). In the present study two types of preneoplastic lesions were seen: tubular dysplasia and interstitial cell hyperplasia. The first neoplastic stage consisted of interstitial or blastemal cells aggregated in the form of microscopic nodules (tumourlets). In the more advanced tumours the blastemal pattern was the more predominant, but we also observed other patterns of epithelial, mesenchymal or neural types. These findings were confirmed by ultrastructural analysis, which revealed blastemal-epithelial transitions and mesenchymal and mesonephric features, as well as the presence of neurosecretory granules. The paucity of immunohistochemical studies on these tumours led us to apply a panel of the most frequently used antibodies in diagnostic pathology to 36 cases of our series. There was co-expression of cytokeratins and vimentin, which were the most intensely stained, together with S-100 protein. Further positivities were seen for carcinoembryonic antigen, desmin, neuron-specific enolase and HNK-1. These results lend support to the revised, new histological classification confirmed by the ultrastructural findings, allowing us to postulate a tumoural origin in the renal interstitial cells, which may be nephrogenic undifferentiated cells that possess an epithelial, mesenchymal and neuroectodermal phenotype.