HDAC9 and cancer: The existing specific inhibitor of FSP1, iFSP1, is not suitable for use in vivo, because it has off‐target effects at high concentrations, and cannot target FSP1, promoting cell ferroptosis, which limits its clinical transformation.[27] HDAC removes the acetyl group from histone lysine residue, alters its charge, tightens chromatin structure, and inhibits transcriptional expression of genes.[28] HDACi can induce apoptosis, autophagy, necrosis, and ROS generation in cancer cells.