An ultrastructural study of benign and malignant breast epithelial cells. A search for tonofilaments

310 breast lesions were examined by electron microscopy. Tonofilaments were demonstrated in excretory epithelial cells of infiltrating ductal carcinoma (29%), infiltrating lobular carcinomas (27%), fibrocystic disease (18%) and in the normal breast (12%). Tonofilaments were also present in uncommon breast carcinomas, such as mucinous, papillary and medullary carcinomas.