Immunohistochemical analysis of mammary tissue in serial sections. Immunohistochemistry images of the mammary tissue isolated from age-matched (52-week) female multiparous control FVB (normal) mice, and abnormal regions observed in CYT-2 (hyperplasia) and CYT-1 (adenocarcinoma, squamous differentiation, solid tumor) ERBB4 transgenic mice. Stained representative images of the mouse mammary tissue obtained from FVB control (n = 3), CYT-2 with hyperplastic region (n = 1) and CYT-1 (n = 3) carcinoma, and a single 2 cm × 2 cm CYT-1 solid tumor. Tissues were embedded in paraffin sections and stained for hematoxylin and eosin (HE), Masson trichrome (MTC; stains for collagen (blue), nuclei (black) and muscle/keratin (red)), ErbB4, cell proliferation marker Ki-67, signal transducer and activator of transcription 5a (STAT5a), smooth muscle actin (SMA; stains for smooth muscle and myoepithelium), epithelial markers E-Cadherin (E-Cad) and cytokeratin 5/6 (CK5/6), and mesenchymal markers Vimentin (Vim) and p63. Scale bars = 50 μm.