Tazemetostat in Treating Patients With Recurrent Ovarian or Endometrial Cancer

Inclusion Criteria: * Pathologically (histologically or cytologically) proven diagnosis of recurrent or persistent ovarian endometrioid or clear cell carcinoma, OR recurrent or persistent endometrioid endometrial adenocarcinoma; patients with recurrent endometrial cancer must have mismatch repair (MMR) immunohistochemistry completed; if they are found to be mismatch repair deficient, they should be offered treatment with immune checkpoint inhibition before consideration for treatment on trial; primary ovarian tumors must be at least 50% endometrioid or clear cell morphology, or have histologically documented recurrence with at least 50% endometrioid or clear cell morphology; institutional pathology reports must be provided indicating at least 50% endometrioid or clear cell morphology for ovarian tumors (primary or recurrent lesions) * Only patients with recurrent or persistent ovarian clear cell carcinoma (OCCC) with ARID1A pathologic variant or likely pathologic variant mutations per next generation sequencing (NGS) are eligible for entry (20-OCT-2021) * Institutional pathology reports must be provided indicating at least 50% clear cell morphology for ovarian tumors (primary or recurrent lesions) and NGS report must be available for step 1 registration (20-OCT-2021) (09-DEC-2021) * All other eligibility criteria and ineligibility criteria must be met for step 2 registration (20-OCT-2021) (09-DEC-2021) * All patients must have measurable disease as defined by Response…