Recently, enhancer of zeste homologue 2 (EZH2), a member of the PcG protein family, has been linked to the aggressiveness of human cancers, including lymphomas (Raaphorst et al, 2000; van Kemenade et al, 2001; Visser et al, 2001; Dukers et al, 2004), breast cancer (Kleer et al, 2003; Raaphorst et al, 2003) and prostate cancer (Sellers and Loda, 2002; Varambally et al, 2002; Rhodes et al, 2003; Foster et al, 2004). This evidence concerns the gene EZH2 and breast cancer.