The epigenetic modifications can change the state of a part of the DNA by different enzymes such as the histone deacetylases. Dysregulation of the epigenetic mechanisms is associated with the initiation and progression of cancer. The reversibility of this dysregulation in epigenetic modifications makes it an attractive target for cancer therapy and drug discovery scientists. We conducted a computerized Literature search involving human subjects, published in English until December 2017, and indexed through Medical Databases; MEDLINE/PubMed, EMBASE, and Web of Science. We reviewed articles performed for prospective and other types of studies related to histone deacetylases inhibitors which can help cancer patient's status during the therapy. Several investigational drugs for cancer therapy are in clinical trials. Interestingly, US Food and Drug Administration has already approved four histone deacetylases inhibitors drugs for hematological malignancies but not for solid tumors. Currently, different histone deacetylases inhibitors are under study for both hematological and solid tumors as single agents or in combinations. In this review, we will discuss some the approved histone deacetylases inhibitors, and the one in clinical trials.