Study of Pemetrexed+Platinum Chemotherapy With or Without Pembrolizumab (MK-3475) in Participants With First Line Metastatic Nonsquamous Non-small Cell Lung Cancer (MK-3475-189/KEYNOTE-189)-Japan Extension Study

This is a Japan Extension Study of Global Study MK-3475-189 (NCT02578680). This is an efficacy and safety study of pembrolizumab (MK-3475) combined with pemetrexed/platinum chemotherapy versus pemetrexed/platinum chemotherapy alone in adult Japanese participants with advanced or metastatic nonsquamous non-small cell lung cancer (NSCLC) who have not previously received systemic therapy for advanced disease. Participants will be randomly assigned to receive pembrolizumab combined with pemetrexed/platinum (Investigators choice of cisplatin or carboplatin), OR pemetrexed/platinum (Investigators choice of cisplatin or carboplatin). With Amendment 11 (effective date 31-Jan-2022), once the study objectives have been met or the study has ended, participants will be discontinued from this study and will be enrolled in an extension study to continue protocol-defined assessments and treatment. The primary hypothesis is that pembrolizumab in combination with pemetrexed/platinum chemotherapy prolongs Progression-Free Survival (PFS) and Overall Survival (OS) compared to pemetrexed/platinum chemotherapy alone.