EZH2 and neoplasm: EZH2 (Enhancer of Zeste Homolog 2) is a subunit of polycomb repressive complex 2 (PRC2), that catalyzes the trimethylation of histone H3 at lysine 27 (H3K27me3), which represses expression of genes such as GSK3B, TP53 (tumor suppressors) (1) and CXCR4 (tumor-promoter) (2).