Changes in gene expression caused by epigenetic alterations in cancer can be divided into three categories, transcriptional regression by methylation of the promoter CpG islands (lesions in the genome rich in sequences consisting of a cytosine preceding a guanine), increased gene expression by hypomethylation, and decreased gene expression associated with histone deacetylase (HDAC) [62–64]. The gene discussed is HDAC9; the disease is cancer.