Tazemetostat in Malignant Peripheral Nerve Sheath Tumors

Inclusion Criteria: * A histologic confirmation of recurrent/refractory and/or metastatic malignant peripheral nerve sheath tumor with Response Evaluation Criteria in Solid Tumors (RECIST) measurable disease * Patients ≥ 12 years of age at the time of enrollment * Performance status: 12-15 years old: Lansky \> 50; 16-17 years old: Karnofsky \> 50; ≥ 18 years old: Eastern Cooperative Group (ECOG) score 0-2 * Subjects must have adequately recovered from the acute toxic effects of all prior anti-cancer therapy per enrolling physician and must meet the following minimum duration from prior anti-cancer directed therapy prior to enrollment. * Anti-cancer agents known to be Myelosuppressive: ≥ 28 days after the last dose of agent. * Anti-cancer agents not known to be myelosuppressive: \> 7 days after the last dose of agent. * Antibodies: \> 21 days must have elapsed from infusion of last dose of antibody, and toxicity related to prior antibody therapy must be recovered to Grade \< 1. * Systemic Corticosteroids: if related to prior therapy \> 14 days must have elapsed, or on stable dose for treatment of CNS disease. * Hematopoietic growth factors: \> 14 days after the last dose of a long-acting growth factor. * Interleukins, Interferons, and Cytokines (other than hematopoietic growth factors): \> 21 days after the completion of interleukins, interferon or cytokines (other than hematopoietic growth factors). * Radiation therapy (XRT)/External Beam Irradiation including…