HDAC9 and plasma cell myeloma: Although the influence of HDAC6 in cancer is not as well investigated as for HDAC1 and HDAC2, HDAC6 has been reported to be up-regulated in oral squamous cell carcinoma and the inhibition of HDAC6 has been reported to induce cytotoxicity in multiple myeloma cells as well as to reduce the amount of Bcr-Abl in leukaemia cells.42–44 The presumptive role of HDACs in malignant diseases has resulted in widespread development of HDAC inhibitors.