HDAC inhibition causes acetylation of nuclear histones, leading to transcriptional activation of several key tumor-related genes, such as the cyclin-dependent kinase inhibitor p21WAF1/CIP1, p53, GATA-1 and estrogen receptor-α, which contribute to inhibiting cancer proliferation and inducing differentiation both in vitro and in vivo [76,77]. Here, HDAC9 is linked to cancer.