Pembrolizumab in Relapsed or Refractory Primary Mediastinal Large B-Cell Lymphoma: Final Analysis of KEYNOTE-170.

Previous analyses of the phase 2 KEYNOTE-170 (NCT02576990) study demonstrated effective antitumor activity and acceptable safety of pembrolizumab 200 mg given every 3 weeks for up to 35 cycles (~2 years) in patients with relapsed/refractory (R/R) primary mediastinal B-cell lymphoma (PMBCL) whose disease progressed after or who were ineligible for autologous stem cell transplantation. End points included objective response rate (ORR), progression-free survival (PFS), and duration of response (DOR) by investigator per 2007 Response Criteria; overall survival (OS); and safety. In this final analysis, median duration of follow-up was 48.7 months (range, 41.2-56.2). ORR was 41.5% (complete response, 20.8%; partial response, 20.8%). Median DOR was not reached; no patients who achieved complete response had progressed at the data cutoff. Median PFS was 4.3 months; 4-year PFS rate was 33.0%. Median OS was 22.3 months; 4-year OS rate was 45.3%. At the data cutoff, 30 patients (56.6%) had any-grade treatment-related adverse events (AEs); the most common were neutropenia, asthenia, and hypothyroidism. Grade 3 or 4 treatment-related AEs occurred in 22.6% of patients; no grade 5 AEs occurred. After 4 years of follow-up, pembrolizumab continued to provide durable responses, with promising trends for long-term survival and acceptable safety in R/R PMBCL.