Pembrolizumab (MK-3475) Versus Placebo Following Surgery and Radiation in Participants With Locally Advanced Cutaneous Squamous Cell Carcinoma (MK-3475-630/KEYNOTE-630)

Inclusion Criteria: Inclusion Criteria include, but are not limited to: * Has histologically confirmed cutaneous squamous cell carcinoma (cSCC) as the primary site of malignancy (metastatic skin involvement from another type of primary cancer or from an unknown primary cancer is not permitted) * Has histologically confirmed locally advanced cutaneous squamous cell carcinoma (LA cSCC) with ≥1 high-risk feature(s) as the primary site of malignancy * Has undergone complete macroscopic resection of all known cSCC disease with or without microscopic positive margins. For those participants with residual microscopic positive margin involvement, confirmation that additional re-excision is not possible must be provided * Has completed adjuvant radiotherapy (RT) for LA cSCC with last dose of RT ≥4 weeks and ≤16 weeks from randomization * Has received an adequate post-op dose of RT (either hypofractionated or conventional) * Is disease free as assessed by the investigator with complete radiographic staging assessment ≤28 days from randomization * Is not pregnant or breastfeeding * Is not a person of childbearing potential (POCBP) * Has a negative pregnancy test ≤72 hours before the first dose of study intervention. * Has provided an archival or newly-obtained tumor tissue sample adequate for Programmed Cell Death Ligand 1 (PD-L1) testing as determined by central laboratory testing * Has a life expectancy of \>3 months * Has an Eastern Cooperative Oncology Group (ECOG) performance sta…