MBD2 and breast neoplasm: To determine the role of Mbd2 in a mouse model with a relatively faithful representation of breast tumor progression, we used a transgenic MMTV-PyMT (mouse mammary tumor virus-polyoma middle tumor-antigen) model, in which the spontaneous and pregnancy-independent expression of the PyMT oncoprotein results in the synchronous appearance of multifocal breast tumors that metastasize predominantly to the lung19,20.