In vitro examination of multiple HDAC inhibitors, including entinostat, combined with capecitabine in breast cancer cell lines (MCF-7, MDA-MD-231, and MDA-MD-468) has shown time- and dose-dependent induction of thymidine phosphorylase and a synergistic antiproliferative effect [12, 13]. The gene discussed is HDAC9; the disease is breast cancer.