MUC1 expression in the canine normal mammary gland and in benign and malignant mammary lesions. Sections of specimens stained immunohistochemically. MUC1 immunoreactivity was present in normal tissues samples, showing luminal and apical expression (A). Moderate and heterogeneous labelling of epithelial cells in complex adenoma (B). Higher level of immunoreactivity in complex carcinoma (C), in cancer cells invading the adipose tissue (D), in simple carcinoma (E) and in intra lymphatic metastatic cells (F). The images were digitalised using a video camera connected to a microscope (DMR Fluo HC, Leica, USA), and the semi-quantitative evaluation was estimated by counting 1.000 positive cells in randomly selected fields (magnification 200x) avoiding necrosis.