Armand P, Rodig S, Melnichenko V, et al. - In the phase IB KEYNOTE-013 and phase II KEYNOTE-170 studies, adults with primary mediastinal large B-cell lymphoma (rrPMBCL) received pembrolizumab for up to 2 years or until disease progression or unacceptable toxicity in order to test the hypothesis that PMBCL was susceptive to programmed cell death-1 (PD-1) blockade. Among 21 individuals in KEYNOTE-013 and 53 in KEYNOTE-170, the objective response rate was 48% (7 complete responses) and 45% (7 complete responses), respectively. No individual with a complete response had progression, including two individuals with a comprehensive response for at least 1 year off therapy. In 24% of patients in KEYNOTE-013 and 23% of patients in KEYNOTE-170, the occurrence of treatment-related adverse events was noted. No treatment-related deaths were seen. The magnitude of the 9p24 gene abnormality was related to PD-L1 expression amongst 42 assessable individuals, which was itself notably related to progression-free survival. Hence, in individuals with rrPMBCL, pembrolizumab was concluded to be related to a high response rate, durable activity, and a flexible safety profile.