In the current work, we investigated the relative expression profiles of 10 HDAC isoenzymes comprising the classes I–III (HDAC1/2/4/6; Sirt1/2/3/5/6/7) in a panel of 17 cancer cell lines, including the breast, cervix, oesophageal, lung, oral squamous, pancreas, as well as urinary bladder carcinoma cells. The gene discussed is HDAC9; the disease is cancer.