Combination of HDAC inhibitors and retinoids is associated with restoration of RARβ in tumours with a partially methylated promoter and greater antitumour activity as compared with single agents (Sirchia et al, 2000; Widschwendter et al, 2000; Pili et al, 2001; Touma et al, 2005; Wang et al, 2005; Kato et al, 2007). Here, HDAC9 is linked to neoplasm.