There are currently no data on maintenance therapy with PD1/PDL1 inhibitors in NSCLC. After an initial response / stable disease to first line chemotherapy, non progressors / candidates for maintenance treatment, represent an ideal setting / patient group to test the efficacy of Pembrolizumab given that chemotherapy results in antigen release, hence it has the potential to augment immune checkpoint blockade, and following disease cytoreduction, this represents a lower disease burden setting, that may suit checkpoint inhibition better given the recent studies in Prostate cancer with Ipilimumab and Melanoma with Pembrolizumab(suggesting better outcomes for patients with less extensive disease).