Granular cell foci of the uterus in donryu rats

Eleven cases of uterine granular cell foci were observed in a total of 855 female Donryu rats. All the lesions were microscopical and focal or multifocal in nature, and composed of uniformly large cells with abundant granulated eosinophilic cytoplasm. Histopathologically, immunohistochemically and ultrastructurally they resembled granular cell tumours of the uterus reported in rats and mice. The development of granular cell foci may be the result of hormonal stimulation.