Purpose

This is a 2 part study. Part 1 is to evaluate the efficacy and safety of dostarlimab plus carboplatin-paclitaxel followed by dostarlimab versus placebo plus carboplatin-paclitaxel followed by placebo; and Part 2 is to evaluate the efficacy and safety of dostarlimab plus carboplatin-paclitaxel followed by dostarlimab plus niraparib versus placebo plus carboplatin-paclitaxel followed by placebo in participants with recurrent or primary advanced (Stage III or IV) endometrial cancer.