[Malignant oncocytoma of the mammary gland]

Described in this paper is the morphological pattern of a malignant oncocytoma in the breast of a woman aged 70 years. The tumour parenchyma consisted mainly of epithelial cells grouped in nests or cords and surrounded by sparse fibrous stroma. The cells were quite large and pleomorphic, their nuclei being round or bizarre with prominent nucleoli. Electron microscopy revealed a conspicuously increased number of mitochondria and bundles of intracytoplasmic microfilaments.