EZH2 and breast cancer: Enhancer of zeste homolog 2 (EZH2), a polycomb group (PcG) protein, is an enzymatic catalytic subunit of PRC2 that regulates gene expression through catalyzing primarily tri-methylation of histone H3 Lys-27 (H3K27), and it functions in the development and progression of a variety of cancers, such as breast cancer (Bachmann et al., 2006), GC (Gan et al., 2018), and NPC (Duan et al., 2020).