PRDM9 and breast cancer: EZH2 gene, a histone methyltransferase gene and an important member of polycomb group (PcG), has been reported to be closely related to the formation and development of a variety of primary tumors (breast cancer included) and can play a role in the regulation of PcG through construction of polycomb-repressive complex 2 (PRC2) and in the modification of epigenetic genes [11,19].