It was revealed that the recovery percentages of IP/INPUT, indicating the binding of c-Myc to the CD26 promoter via the proximal G-C box was exposure time-dependently decreased on treatment with HDACi, whereas the binding of c-MycK323ac to the promoter showed a time-dependent increase in each myeloma cell line following treatment with HDACi. This evidence concerns the gene DPP4 and plasma cell myeloma.