The purpose of this study is to assess the safety and efficacy of treatment with pembrolizumab (MK-3475) compared to a combination of carboplatin and paclitaxel in women with mismatch repair deficient (dMMR) advanced or recurrent endometrial carcinoma who have not previously been treated with prior systemic chemotherapy. The primary study hypotheses are that pembrolizumab is superior to the combination of carboplatin and paclitaxel with respect to Progression Free Survival (PFS) per Response Evaluation Criteria in Solid Tumors Version 1.1 (RECIST 1.1) as assessed by Blinded Independent Central Review (BICR) and Overall Survival (OS).