The company said patients taking the FDA-approved 2 milligram dosage of Keytruda and those taking an experimental 10 milligram dose had longer overall survival compared with those taking docetaxel, a commonly used chemotherapy.
The randomized, pivotal Phase 2/3 trial has therefore met its primary objective.
Treatment with Keytruda, at both doses, also provided superior progression-free survival (PFS) when compared to that achieved after treatment with docetaxel in patients whose tumors had tumor proportion scores values equal to or more than 50%.
Merck said safety of Keytruda was consistent with what had been seen in earlier studies among advanced non-small-cell lung cancer patients (NSCLC).
Merck Research Laboratories president Roger Perlmutter said: "The results from this trial provide part of a growing body of evidence supporting the potential of Keytruda in the treatment of non-small-cell lung cancer."
The company plans regulatory submissions in the US in late 2015 and in the European Union in early next year.
In lung cancer, Keytruda is indicated in the US at a dose of 2 mg/kg administered as an intravenous infusion over 30 minutes every three weeks to treat metastatic NSCLC patients whose tumors express PD-L1 as determined by an FDA-approved test with disease progression on or after platinum-containing chemotherapy.
Patients with EGFR or ALK genomic tumor aberrations should have disease progression on FDA-approved therapy for the aberrations before receiving Keytruda.
In melanoma, Keytruda is indicated to treat patients with unresectable or metastatic melanoma and disease progression after ipilimumab and, if BRAF V600 mutation positive, a BRAF inhibitor.