The present invention is directed to tricyclic compounds of formula (I) which are inhibitors of one or more mutant IDH enzymes (I); wherein A is -C(R1)= or -N=; and X is selected from the group consisting of : (II-i), and (II-ii). The present invention is also directed to uses of the tricyclic compounds described herein in the potential treatment or prevention of cancers in which one or more mutant IDH enzymes are involved. The present invention is also directed to compositions comprising these compounds. The present invention is also directed to uses of these compositions in the potential prevention or treatment of such cancers.