Safety and Efficacy of Pembrolizumab Compared to Placebo in Resected High-risk Stage II Melanoma (MK-3475-716/KEYNOTE-716)

This 2‐part study will evaluate the safety and efficacy of pembrolizumab (MK‐3475) compared to placebo in participants with surgically resected high‐risk Stage II melanoma. Participants in Part 1 will receive either pembrolizumab or placebo in a double‐blind design every 3 weeks (Q3W) for up to 17 cycles/ 1 year (each cycle = 21 days). Participants who complete the initial treatment of 17 cycles of pembrolizumab in Part 1 and experience disease recurrence may be eligible for re‐challenge with pembrolizumab at the same dose and schedule of 200 mg Q3W (21‐day cycles) for up to 35 cycles (up to 2 years) in Part 2 in an open label design. Participants who complete the initial treatment of placebo and experience disease recurrence may be eligible to switch over to pembrolizumab 200 mg Q3W (21‐day cycles) for up to 35 cycles (up to 2 years) in Part 2 in an open label design. The primary hypothesis of this study is that pembrolizumab increases recurrence‐free survival (RFS) compared to placebo. Per protocol, response/ progression or adverse events (AEs) during re‐challenge/switch‐over in Part 2 will not be counted towards the RFS outcome measure or safety outcome measures respectively.