Efficacy and Safety Study of Stereotactic Body Radiotherapy (SBRT) With or Without Pembrolizumab (MK-3475) in Adults With Unresected Stage I or II Non-Small Cell Lung Cancer (NSCLC) (MK-3475-867/KEYNOTE-867)

The purpose of this study is to assess the efficacy and safety of stereotactic body radiotherapy (SBRT) plus pembrolizumab (MK-3475) in the treatment of adult participants with unresected stage I or II (Stage IIB N0, M0) non-small cell lung cancer (NSCLC). The primary study hypotheses are: SBRT plus pembrolizumab prolongs Event-free Survival (EFS) compared to SBRT plus placebo (normal saline solution), and SBRT plus pembrolizumab prolongs Overall Survival (OS) compared to SBRT plus placebo.