The histone lysine demethylase (KDM) 4 (Jmj-D2) subfamily of KDMs (Kooistra and Helin, 2012; Black et al., 2013), which are up-regulated in many cancer cell types (Franci et al., 2014), show a preference for demethylation of tri- and di-Nε-methylated H3K9 substrates, with KDM4A-C also acting on H3K36 (Berry and Janknecht, 2013). This evidence concerns the gene KDM4A and cancer.