HDAC9 and cancer: Epigenetic reprogramming, which includes modification of histones, is firmly associated with tumor progression; aberrant repression of transcriptional activity is a common feature of various types of cancer.[45] Furthermore, using HDAC inhibitors to enhance histone acetylation increases the efficacy of anti‐cancer therapies.[46, 47] SCFAs inhibit HDAC, representing another mechanism by which they regulate the TME.[48] Through inhibiting HDAC, butyrate produced by gut commensal microbes, increases the expression of Foxp3 in CD4+ T cells.