The present invention relates to a method of treating cancer in a subject in need thereof, by administering to a subject in need thereof a first amount of a histone deacetylase (HDAC) inhibitor or a pharmaceutically acceptable salt or hydrate thereof, and a second amount of an anti-cancer agent. The HDAC inhibitor and the anti-cancer agent may be administered to comprise therapeutically effective amounts. In various aspects, the effect of the HDAC inhibitor and the anti-cancer agent may be additive or synergistic.