Entinostat plays an important role in histone acetylation/deacetylation in nucleosomes, mainly by inhibiting histone deacetylation and promoting the expression of blood and cancer cell genes in vivo and in vitro. Entinol induces the expression of p21WAF-1/CIP-1 gene independently of p53 activity. A number of in vitro and in vivo studies have demonstrated antitumor activity of entinol. Entinostat is a novel oral HDAC1 inhibitor with a safety and efficacy profile, both as a single agent and in combination with commercially available targeted therapies, that sets it apart from other HDAC inhibitors. Preclinical, Phase I and Phase II clinical trials have also confirmed the safety and efficacy of this product, and the FDA designated this product as a breakthrough therapy based on the results of one of its Phase II clinical trials. Phase III clinical trials have also begun, and we look forward to the results of subsequent trials. If the expected results can be obtained in phase III clinical trials, it will solve the unmet clinical drug needs and bring more survival benefits to a large number of advanced breast cancer patients.