Inclusion Criteria:

• Has demonstrated clinical benefit from treatment with tazemetostat.
• Is currently receiving tazemetostat as either monotherapy or in combination with other approved drug(s) or investigational agent(s) on an Epizyme-sponsored clinical trial or any other clinical trial being conducted with tazemetostat that is not sponsored by Epizyme (including but not limited to, Investigator initiated trials). For subjects on combination therapy, the other therapeutic(s) must have been completed or will be provided by a source other than Epizyme.
• Has provided signed written informed consent.
• Has a life expectancy of > 3 months.
• Has adequate hematopoietic, coagulation, renal and hepatic function. Subject must remain eligible for continued treatment with tazemetostat according to the eligibility and treatment criteria from the antecedent study.
• For French subjects only: Is either affiliated with or a beneficiary of a social security category.
• Female subjects of childbearing potential must:
  • Have a negative beta-human chorionic gonadotropin (β-hCG) pregnancy test at time of study entry and within 14 days prior to planned first dose of investigational product; and 
  • Agree to use effective contraception until 30 days following the last dose of investigational product and have a male partner who uses a condom; or 
  • Practice true abstinence; or
  • Have a male partner who is vasectomized.
• Male subjects with a female partner of childbearing potential must: 
  • Be vasectomized; or 
  • Agree to use condoms until 30 days following the last dose of investigational product; or 
  • Have a female partner who is NOT of childbearing potential.

Exclusion Criteria:

• Has had an interruption of tazemetostat dosing of >14 days from the antecedent clinical study to starting the rollover study unless approved by Medical Monitor.
• Has any other malignancy other than the one for which they are receiving tazemetostat Exception: Subject who has been disease-free of a prior malignancy for 5 years, or subject with a history of a completely resected non-melanoma skin cancer or successfully treated in situ carcinoma is eligible.
• Has thrombocytopenia, neutropenia, or anemia of Grade ≥3 (per CTCAE 4.03 criteria) or any prior history of myeloid malignancies, including myelodysplastic syndrome (MDS).
• Has a prior history of T-LBL/T-ALL.
• Is unwilling to exclude grapefruit juice, Seville oranges and grapefruit from the diet and all foods that contain those fruits from time of enrollment to while on study.
• Is currently taking any prohibited medication(s).
• Is unable to take oral medications, malabsorption syndrome or any other uncontrolled gastrointestinal condition (e.g., nausea, diarrhea or vomiting) that might impair the bioavailability of tazemetostat.
• Has an uncontrolled intercurrent illness including, but not limited to, uncontrolled infection, or psychiatric illness/social situations that would limit compliance with study requirements.
• For female subjects of childbearing potential: Is pregnant or nursing 10. Has been permanently discontinued from tazemetostat therapy due to adverse event, intolerance or treatment failure