MBD2 and breast cancer: To understand the role of Mbd2 in mammary tumor growth and metastasis, we first generated PyMT-Mbd2−/− (homozygous Mbd2-KO) mice on a C57BL/6 background using the crossbreeding strategy described in the “Materials and Methods” section and confirmed the deletion of Mbd2 gene in the primary tumors by qPCR (Fig. 2a).