A. Immunohistochemical analysis of four groups mice. H&E staining of breast in mice from C57BL/6J group, C57BL/6J + E2 group, C57BL/6J-CYP1B1 group and C57BL/6J-CYP1B1 + E2 group. 400×, bar = 50 μm. B. Representative images for H&E staining of breast, liver and lung samples from four groups. B. Expression of ki67 and ER protein in mammary gland of four groups mice. Cells stained brown indicate positive expression. Mammary gland from C57BL/6J group, C57BL/6J + E2 group, C57BL/6J-CYP1B1 group and C57BL/6J-CYP1B1 + E2 group mice were stained for Ki67 and ERα.