Disclosed is a novel type of compounds serving as an EZH2 inhibitor; specifically disclosed are a compound as represented by formula (III) and a pharmaceutically acceptable salt thereof.L'invention concerne un nouveau type de composés servant comme inhibiteur de l'EZH2; plus particulièrement, l'invention concerne un composé tel que représenté par la formule (III) et un sel pharmaceutiquement acceptable de celui-ci.