KDM5A and cancer: The KDM5 subfamily of JmjC-KDMs (KDM5A-D) catalyses demethylation of the transcriptionally activating tri- and di-methylated lysine-4 mark on histone H3 (H3K4me3/2), and is generally associated with transcriptional repression.10, 11, 12, 13 The KDM5s are associated with development and progression of multiple cancers,11, 14 and can mediate cancer cell drug tolerance and maintain tumour-initiating cells.15, 16 KDM5A/B have three PHD-fingers (PHD1-3, numbered sequentially from the N-terminus), whereas KDM5C/D have two.