HDAC9 and neoplasm: There is preclinical evidence that overexpression of HDAC has been found in MM, while inhibition of HDAC leads to the blockade of aggresome and ubiquitin-proteasome pathways and increased acetylation of histone proteins, which regulate the expression of tumor suppressor genes and transcriptional factors, elucidating the synergistic antimyeloma effect of bortezomib and HDACi when used in combination [9, 10].