Tazemetostat+Nivo/Ipi in INI1-Neg/SMARCA4-Def Tumors

Inclusion Criteria: * Diagnosis: Histologically confirmed tumors at diagnosis or at relapse (as applicable): * Stratum A * Atypical Teratoid Rhabdoid Tumor (ATRT) * Other INI1- or SMARCA4-deficient primary CNS malignant tumors (with PI approval) * Stratum B * Malignant rhabdoid tumor (MRT) * Rhabdoid tumor of the kidney (RTK) * Epithelioid sarcoma * Chordoma (poorly differentiated or de-differentiated) * Other INI1- or SMARCA4-deficient malignant tumors (with PI approval) * All subjects must have had tumor assessment at original diagnosis or relapse showing either of the following: Loss of INI1 confirmed by immunohistochemistry (IHC) OR molecular confirmation of tumor bi-allelic SMARCB1 (INI1) loss or mutation when INI1 IHC is equivocal or unavailable * Loss of SMARCA4 confirmed by IHC OR molecular confirmation of tumor SMARCA4 loss or mutation (with PI approval) Reports confirming these findings (including tumor sequencing if available) will be reviewed by the Sponsor-Investigator, PI or designee for approval of eligibility prior to enrollment. * Treatment status: All subjects must have completed planned upfront treatment for their disease for strata A1 or B1. Subjects need not have relapsed or have refractory disease to be eligible for this protocol. * Disease Status: For subjects under consideration for strata A1 or B1, subjects must have evaluable disease Note: Leptomeningeal lesions/disease are allowed as evaluable disease. * For relapsed/refractory subj…