Purpose

This is a study of the safety and efficacy of adavosertib in combination with paclitaxel plus carboplatin in the treatment of ovarian, fallopian tube, and primary peritoneal tumors with the P53 mutation. In Part 1, a small group of participants will receive adavosertib along with paclitaxel plus carboplatin to establish the tolerability of adavosertib with this combination. In Part 2, participants will be randomly assigned to receive either adavosertib plus paclitaxel and carboplatin OR placebo plus paclitaxel and carboplatin to assess efficacy of adavosertib compared to placebo. The primary hypothesis of the study (Part 2) is that administration of adavosertib in combination with paclitaxel plus carboplatin in participants with platinum sensitive p53 mutant ovarian cancer will result in improvement in progression free survival (PFS) per enhanced Response Evaluation Criteria In Solid Tumors version 1.1 (enhanced RECIST 1.1) compared to participants treated with paclitaxel plus carboplatin alone.