This is a phase I, multi-center, open-label, multi-dose, two-part PK and safety study to characterize the DDI potential of oral Tazemetostat. Detailed Description: This two-part study is designed to characterize the steady-state PK of oral Tazemetostat and its metabolite EPZ 6930 when administered as a single and twice daily dose in subjects with advanced malignancies while taken alone or in combination with either itraconazole or rifampin. Part 1: Tazemetostat and Itraconazole Drug Interaction Part 1 of the study will evaluate the drug-drug interaction between Tazemetostat and itraconazole in an open-label, fixed sequential cross over design. Part 2: Tazemetostat and Rifampin Drug Interaction Part 2 of the study will evaluate the drug-drug interaction between Tazemetostat and rifampin in an open-label, fixed sequential cross over design. For both Parts 1 and 2, safety and tolerability will be assessed throughout the subject’s participation. Subjects must have an end of study visit after 30 days of the last dose of Tazemetostat for safety assessment.