The observation that gain-of-function mutations in the EZH2 gene and overexpression of EZH2 protein are frequently found in a wide variety of cancers and that those events often correlate with high-grade cancer progression and/or a poor prognosis has stimulated interest in the development of EZH2 inhibitors to use as therapeutic agents to treat cancer [7–11]. This evidence concerns the gene EZH2 and cancer.