In this aspirate of a mass in the mammary gland of a dog, there are tightly adherent clusters of cuboidal epithelial cells with central to eccentric nuclei. Cytoplasmic outlines are generally sharp and distinct. The adherent appearance of the cells indicates an epithelial origin. In this case, there were many epithelial cell clusters (more than expected for aspiration of normal mammary tissue) and a mammary tumor was diagnosed on cytology. The tumor cells do not display prominent criteria of malignancy (there is mild anisokaryosis). Histopathologic examination is generally needed to ascertain the malignant nature of mammary tumors in dogs (wright’s stain, 50x objective)
