Tazemetostat Plus CHOP in 1L T-cell Lymphoma

Inclusion Criteria: * Participants must have histologically or cytologically confirmed peripheral T cell lymphoma of one of the following subtypes: PTCL-NOS, Follicular helper T-cell lymphoma (ICC 2022) or Nodal T-follicular helper (TFH) cell lymphoma by (WHO 2022) which includes follicular helper T-cell lymphoma, AITL and follicular helper T cell lymphoma, follicular type, EATL, MEITL. All pathology will be reviewed at BWH. BWH review is not required prior to enrollment and patients may be enrolled based upon local pathology analysis. Ten blank slides will be required from outside tumor biopsy for correlative studies. * No prior treatment for T NHL with the exception of one cycle of CHOP or CHOEP or 7 days of corticosteroids at a dose of up to prednisone 60 mg or equivalent for palliation of disease related symptoms so long as the corticosteroids are discontinued prior to tazemetostat prephase or cycle 1 of treatment if not receiving the prephase. * At least one bi-dimensionally measurable lesion, defined as \>1.5 cm in its longest dimension as measured by CT. * Age ≥18 years. * ECOG performance status ≤2 (Karnofsky ≥60%, see Appendix A). * Participants must have adequate organ and marrow function as defined below: * absolute neutrophil count ≥1,000/mcL (750 mcl if bone marrow involvement with lymphoma) * platelets ≥75,000/mcL (25,000 if bone marrow involvement with lymphoma) * total bilirubin ≤ institutional upper limit of normal (ULN) * AST(SGOT)/ALT(SGPT) ≤3 × institutional ULN * creatinine ≤ 1.5 x institutional ULN OR * glomerular filtration rate (GFR) ≥60 mL/min/1.73 m2 * Because the effects of tazemetostat on human immunodeficiency virus (HIV)-infected participants and anti-retroviral therapy is unknown, patients with known HIV infection are not eligible for this trial. * For participants with evidence of chronic hepatitis B virus (HBV) infection, the HBV viral load must be undetectable on suppressive therapy, if indicated. * Participants with a history of hepatitis C virus (HCV) infection must have been treated and cured. Participants with HCV infection who are currently on treatment, are not eligible. * Left ventricular ejection fraction of \> 50% as assessed by echocardiography or multi-gate acquisition (MUGA) scan. * The effects of tazemetostat on the developing human fetus are unknown. For this reason and because other therapeutic agents used in this trial are known to be teratogenic, women of child-bearing potential and men must agree to use adequate contraception (hormonal or barrier method of birth control; abstinence) prior to study entry and for the duration of study participation. Should a woman become pregnant or suspect she is pregnant while she or her partner is participating in this study, she should inform her treating physician immediately. For women of childbearing potential, a negative serum pregnancy test result within 7 days prior to commencement of dosing. Women who are considered not to be of childbearing potential are not required to have a pregnancy test. * Men treated or enrolled on this protocol must also agree to use adequate contraception prior to the study, for the duration of study participation, and 3 months after completion of tazemetostat administration.Women should use effective contraceptive methods beginning ≥28 days prior to initiating, during tazemetostat treatment, and for at least 6 months after the final dose of tazemetostat * Ability to understand and the willingness to sign a written informed consent document. Exclusion Criteria: * Participants who have had chemotherapy for T cell lymphoma prior to entering the study (except 1 cycle of CHOP/CHOEP as noted above). Prior radiotherapy may be allowed after discussion with the sponsor-investigator so long as the area radiated was not the only measurable site of disease. * Participants who are receiving any other investigational agents. * Patients with known central nervous system involvement with lymphoma * History of allergic reactions attributed to compounds of similar chemical or biologic composition to tazemetostat or other agents used in study. * Prior organ transplantation. * Current motor or peripheral neuropathy with grade \>1. * History of other malignancy that could affect compliance with the protocol or interpretation of results. Exceptions include: * Patients with a history of curatively treated basal or squamous cell carcinoma or melanoma of the skin or in situ carcinoma of the cervix at any time prior to the study are eligible. * Patients with any malignancy appropriately treated with curative intent and the malignancy has been in remission without treatment for \> 2 years prior to enrollment are eligible. * Patients with low-grade, early-stage prostate cancer (Gleason score 6, Stage 1 or 2) with no requirement for therapy at any time prior to study are eligible. * Uncontrolled intercurrent illness. * Pregnant women and women intending to become pregnant are excluded from this study because chemotherapeutic agents used in this study have the potential for teratogenic or abortifacient effects. Because there is an unknown but potential risk for adverse events in nursing infants secondary to treatment of the mother with tazemetostat, breastfeeding should be discontinued if the mother is treated with tazemetostat. * Evidence of significant, uncontrolled, concomitant diseases that could affect compliance with the protocol or interpretation of results, including significant cardiovascular disease (such as New York Heart Association Class III or IV cardiac disease, myocardial infarction within the last 6 months, unstable arrhythmias, or unstable angina) * Recent major surgery (within 4 weeks prior to the start of Cycle 1), other than for diagnosis * Known active bacterial, viral, fungal, mycobacterial, parasitic, or other infection (excluding fungal infections of nail beds) at study enrollment or significant infections within 2 weeks before the start of Cycle 1. * Inability to swallow pills. * Because no dosing or adverse event data are currently available on the use of tazemetostat in combination with CHOP in participants \<18 years of age, children are excluded from this study, but will be eligible for future pediatric trials.