Tazemetostat in Treating Patients With Recurrent Ovarian or Endometrial Cancer

PRIMARY OBJECTIVES: I. To assess the clinical activity (overall response rate) of tazemetostat in patients with recurrent or persistent endometrioid or clear cell ovarian carcinoma, and patients with recurrent or persistent endometrioid endometrial adenocarcinoma. II. To assess the clinical activity (response frequency) of tazemetostat in patients with recurrent or persistent clear cell ovarian carcinoma with an ARID1A mutation. SECONDARY OBJECTIVES: I. To examine the nature and degree of toxicity in patients with this regimen. II. To examine the progression free survival and overall survival for this patient population receiving tazemetostat. III. To examine the 6 month clinical benefit rate in patients treated with this regimen. (20-OCT-2021) IV. To evaluate BAF250a expression in patient samples as an indicator of ARID1A mutation status and correlation with the clinical response to study drug. Note: this only applies to patients enrolled prior to the 20-OCT-2021 version date. (20-OCT-2021) EXPLORATORY OBJECTIVES: I. Whether or not the patient has an ARID1A mutation. (08/13/2019) Note: this only applies to patients enrolled prior to the 20-OCT-2021 version date. (20-OCT-2021) (Translational Research Integrated Objective) II. To examine the correlation between ARID1A mutation and BAF250a expression and to identify potential mutations predictive of response in patients with preserved BAF250a expression. Note: this only applies to patients enrolled prior to the 20-OCT-2021 version date. (20-OCT-2021) OUTLINE: Patients receive tazemetostat orally (PO) twice daily (BID) on days 1-28. Cycles repeat every 28 days in the absence of disease progression or unacceptable toxicity. Patients also undergo computed tomography (CT) scans and magnetic resonance imaging (MRI) on study. After completion of study treatment, patients are followed up every 3 months for 2 years and then every 6 months for 3 years.