Histopathological analyses of the mammary gland carcinomas developed in STAT1-/- mice. Histopathological analyses of the early lesions (A-H) and the invasive adenocarcinomas (I-N) in mammary glands of STAT1-/- mice. (A, B) Whole-mount images of a thoracic mammary fat pad show aberrant dilation of mammary ducts and clusters of cystic alveoli (arrow and arrowhead). Panel (B) is a magnified image of panel (A). Scale bars = 1 mm. (C-H) Histology of the cluster of cysts shown in panel (B), highlighted by an arrow in panel (B), demonstrated mammary intraepithelial neoplasia (MIN). (C, D, I, J) Sections were stained with hematoxylin and eosin (H&E). Solid nests of neoplastic cells with areas of necrosis and invasion are evident in the carcinomas (I, J). (E-H, K-N) Atypical cells in MIN lesion and neoplastic cells expressed estrogen receptor-alpha (ERα) (E, F, K, L) and progesterone receptor (PR) (G, H, M, N). (C, E, G, I, K, M) Scale bars = 100 μm. (D, F, H, J, L, N) Higher magnification of the corresponding left panels. Scale bars = 40 μm.