Dostarlimab will be administered through a 30 minute infusion at a dose of 500 milligrams (mg) intravenously (IV) every 3 weeks (Q3W) up to a maximum of 35 cycles (each cycle of 21 days).
Pembrolizumab will be administered through a 30 minute infusion at a dose of 200 mg Q3W up to a maximum of 35 cycles (each cycle of 21 days).
Pemetrexed will be administered at 500 milligram per meter square (mg/m^2 ) IV through a 10 minute IV infusion Q3W, up to a maximum of 35 cycles (each cycle of 21 days).
Cisplatin will be administered at 75 mg/m^2 through a 30 minute IV infusion Q3W for 4 cycles (each cycle of 21 days) as per investigator decision.
Carboplatin will also be administered at area under the concentration time curve 5 milligram/milliliters/minute (mg/mL/min) (maximum dose: 750 mg) through a 15 to 60 minute IV infusion Q3W for 4 cycles (each cycle of 21 days) as per investigator decision.