Additional Study Information: The study drug (TSR-042) in this study is designed to stop cancer from growing by helping your immune system recognize and fight the cancer. The Study Drug is designed to help your immune system by attaching to a protein called PD-1 and stopping one of the signals that keeps your immune system from recognizing the cancer. This may help your immune system attack and destroy the cancer cells. Other drugs that work in a similar way have already been approved in some countries and are in use in some forms of skin, lung, kidney, blood, bladder and head and neck cancers.We are enrolling into Part 2B of the study: 1. Histologically or cytologically proven advanced (unresectable) or metastatic solid tumor with measurable lesion(s) defined by RECIST 1.1 and meets one of the following disease type: i. Cohort A1 - Patients with MSI-H endometrial cancer who have progressed on or after at least 1, but no more than 2 lines of anti-cancer therapy (of which, at least 1 must be a platinum-based therapy) known to confer a clinical benefit for advanced or metastatic disease. ii. Cohort A2 Patients with MSS endometrial cancer who have progressed on orafter at least 1, but no more than 2 lines of anti-cancer therapy (of which, at least 1 must be a platinum-based therapy) known to confer a clinical benefit for advanced or metastatic disease. 2. Cohort C - Patients with serous or clear cell ovarian, fallopian tube, or primary peritoneal cancer who have recurrent disease and were previously treated with chemotherapy for advanced/metastatic disease and who are currently considered platinum-resistant or refractory.3. Patients must have archival tumor tissue available that is formalin-fixed and paraffin-embedded slides from archived tumor tissue). TYPES OF CANCER: Endometrial Cancer, Ovarian Cancer, Fallopian Tube Cancer, Primary Peritoneal Cancer