Study of Pemetrexed Platinum Chemotherapy With or ...

Arm Intervention/treatment Experimental: Pembrolizumab

Participants receive pembrolizumab 200 mg intravenously (IV) PLUS pemetrexed 500 mg/m^2 IV (with vitamin supplementation) PLUS cisplatin 75 mg/m^2 IV OR carboplatin Area Under the Curve (AUC) 5 IV on Day 1 of every 3-week cycle (Q3W) for 4 cycles followed by pembrolizumab 200 mg IV PLUS pemetrexed 500 mg/m^2 IV Q3W until progression.

Biological: Pembrolizumab 200 mg

IV infusion

Drug: Cisplatin

IV infusion

Drug: Carboplatin

IV infusion

Drug: Pemetrexed

IV infusion

Dietary Supplement: Folic acid 350-1000 μg

Orally; at least 5 doses of folic acid must be taken during the 7 days preceding the first dose of pemetrexed, and folic acid dosing must continue during the full course of therapy and for 21 days after the last dose of pemetrexed.

Dietary Supplement: Vitamin B12 1000 μg

Intramuscular injection in the week preceding the first dose of pemetrexed and once every 3 cycles thereafter. Subsequent vitamin B12 injections may be given the same day as pemetrexed administration.

Drug: Dexamethasone 4 mg

For prophylaxis; orally twice per day (or equivalent). Taken the day before, day of, and day after pemetrexed administration.

Active Comparator: Control

Participants receive saline placebo IV PLUS pemetrexed 500 mg/m^2 IV (with vitamin supplementation) PLUS cisplatin 75 mg/m^2 IV OR carboplatin AUC 5 IV on Day 1 of every 3-week cycle (Q3W) for 4 cycles followed by saline placebo IV PLUS pemetrexed 500 mg/m^2 IV Q3W until progression. If documented progression occurs, participants may be able to receive pembrolizumab Q3W for the remainder of the study or until documented further progression.

Drug: Cisplatin

IV infusion

Drug: Carboplatin

IV infusion

Drug: Pemetrexed

IV infusion

Dietary Supplement: Folic acid 350-1000 μg

Orally; at least 5 doses of folic acid must be taken during the 7 days preceding the first dose of pemetrexed, and folic acid dosing must continue during the full course of therapy and for 21 days after the last dose of pemetrexed.

Dietary Supplement: Vitamin B12 1000 μg

Intramuscular injection in the week preceding the first dose of pemetrexed and once every 3 cycles thereafter. Subsequent vitamin B12 injections may be given the same day as pemetrexed administration.

Drug: Dexamethasone 4 mg

For prophylaxis; orally twice per day (or equivalent). Taken the day before, day of, and day after pemetrexed administration.

Drug: Saline solution

IV infusion