Pembrolizumab Monotherapy in Relapsed or Refractory Primary Mediastinal Large B-Cell Lymphoma (PMBCL): 3-Year Follow-up of the Keynote-170 Study
Authors: Zinzani Pier Luigi , Melnichenko Vladimir , Bouabdallah Krimo , Walewski Jan , Majlis Alejandro , Fogliatto Laura , Caballero Dolores , Christian Beth A. , Gulbas Zafer , Özcan Muhit , Salles Gilles , Shipp Margaret A. , Thompson Seth , Orlowski Robert J , Marinello Patricia , Armand Philippe 
Published: November 2020

Introduction: No standard of care exists for patients (pts) with relapsed or refractory primary mediastinal B-cell lymphoma (rrPMBCL). As such, pts typically receive therapies recommended for diffuse large B-cell lymphoma, with poor prognosis. Similar to classical Hodgkin lymphoma, rrPMBCL tumors often overexpress the programmed death 1 (PD-1) ligands, PD-L1 and PD-L2. Data from the first full analysis of the phase 2 KEYNOTE (KN)-170 (NCT02576990) study showed that pembrolizumab provided effective and durable antitumor activity with a manageable safety profile in patients with rrPMBCL. These data led to the FDA approval of pembrolizumab for pts with rrPMBCL after ≥2 prior therapies. In this aggressive malignancy with few salvage options, duration of remission with PD-1 blockade remains a critical question. Here we present data from KN170 with an additional 24 months of follow-up in patients with rrPMBCL.
Methods: Pts with rrPMBCL who had relapsed after or were ineligible for autologous stem cell transplant with ≥2 lines of prior therapy were enrolled in KN170 to receive 200 mg pembrolizumab IV Q3W until disease progression or toxicity, for up to 2 years. Tumor response was assessed Q12W with PET/CT scans by IWG 2007 criteria. The primary endpoint was objective response rate (ORR) by blinded independent central review (BICR). Secondary endpoints included duration of response (DOR), progression-free survival (PFS), overall survival (OS), and safety. Exploratory endpoints included response by Lugano 2014 criteria. The data cutoff date for this analysis was May 7, 2020.
Results: At the data cutoff date, among all treated pts (N=53), 13 had completed 2 years of treatment and 40 had discontinued largely due to progression (n=30). The ORR was 45% (24/53; 95% CI 32-60) with a CR rate of 19% (10/53; 13/53 [25%] by Lugano criteria). No patient who achieved CR by BICR had received consolidation therapy or had progressed at data cutoff. After a median study follow-up of 43.1 months (range, 35.6-50.7) the median DOR was not reached (range, 1.1+ to 46.9+ mo); 76% of pts had a response duration ≥36 mo. Median PFS was 5.5 mo (95% CI, 2.7-15.1), with 36-mo PFS rate of 34%. The median OS was 22.3 mo (95% CI, 7.3 to not reached) with 36-mo OS rate of 45%. At data cutoff, 50 (94%) pts had at least one adverse event (AE), with 30 (57%) having a treatment-related AE. The most common treatment-related AEs were neutropenia (19%), asthenia (9%), hypothyroidism (8%), fatigue (6%), and pyrexia (6%). Grade ≥3 treatment-related AEs occurred in 12 (23%) pts. Six (11%) pts had an immune-mediated AE. There were no treatment-related grade 5 events.
Conclusion: Results from the longer-term follow-up of KN170, the largest prospective clinical trial in rrPMBCL, shows that pembrolizumab provides robust and durable antitumor activity with a manageable safety profile in patients with rrPMBCL.

Disclosures
Zinzani: Roche: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; TG Therapeutics, Inc.: Honoraria, Speakers Bureau; Servier: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Janssen: Consultancy, Honoraria, Speakers Bureau; Kirin Kyowa: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; EUSA Pharma: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Janssen-Cilag: Consultancy, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Kyowa Kirin: Consultancy, Speakers Bureau; Immune Design: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Immune Design: Consultancy, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; MSD: Consultancy, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Eusapharma: Consultancy, Speakers Bureau; Celgene: Consultancy, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Verastem: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Sanofi: Consultancy, Membership on an entity's Board of Directors or advisory committees; Sandoz: Consultancy, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Portola: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Merck: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; BMS: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Gilead: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Incyte: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; AbbVie: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; ADC Therapeutics: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Celltrion: Consultancy, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Bouabdallah:Roche: Consultancy, Honoraria; Takeda: Consultancy, Honoraria; Gilead Sciences: Consultancy, Honoraria. Walewski:Roche: Consultancy, Honoraria, Other: travel expenses, Research Funding; GSK/Novartis: Research Funding; Celgene: Consultancy, Honoraria; Takeda: Consultancy, Honoraria; Janssen-Cilag: Consultancy, Honoraria; Servier: Consultancy, Honoraria; Amgen: Consultancy, Honoraria; Abbvie: Consultancy, Honoraria; Gilead: Consultancy, Honoraria; Novartis: Consultancy, Honoraria; Bristol Myers Squibb: Consultancy. Caballero:Gilead: Other: travel; Roche: Other: travel; Janssen: Membership on an entity's Board of Directors or advisory committees, Other: travel; Celgene: Membership on an entity's Board of Directors or advisory committees, Other: travel; Kite: Membership on an entity's Board of Directors or advisory committees; Takeda: Other: travel; BMS: Other: travel. Christian:Acerta: Research Funding; Celgene: Research Funding; Genentech: Research Funding; Merck: Research Funding; Millenium: Research Funding; MorphoSys: Research Funding; F Hoffman-La Roche: Research Funding; Triphase: Research Funding; Seattle Genetics: Membership on an entity's Board of Directors or advisory committees, Research Funding; Verastem: Membership on an entity's Board of Directors or advisory committees; AstraZenica: Membership on an entity's Board of Directors or advisory committees. Özcan:Takeda: Honoraria, Other: travel, Research Funding; Roche: Other: travel, Research Funding; Bayer: Research Funding; Abbvie: Other: travel, Research Funding; Archigen: Research Funding; Celgene: Research Funding; MSD: Research Funding; Novartis: Research Funding; Amgen: Honoraria, Other: travel; BMS: Other; Jazz: Other; Sanofi: Other; Abdi Ibrahim: Other; Janssen: Other: travel, Research Funding. Salles:Bristol Myers Squibb: Consultancy, Other; Takeda: Consultancy, Honoraria, Other; Gilead: Consultancy, Honoraria, Other: Participation in educational events; Debiopharm: Consultancy; Kite: Consultancy, Honoraria, Other; MorphoSys: Consultancy, Honoraria, Other; Janssen: Consultancy, Honoraria, Other: Participation in educational events; Novartis: Consultancy, Honoraria, Other; F. Hoffman-La Roche Ltd: Consultancy, Honoraria, Other; Celgene: Consultancy, Honoraria, Other: Participation in educational events; Epizyme: Consultancy; Karyopharm: Consultancy; Autolus: Consultancy; Amgen: Honoraria, Other: Participation in educational events; Abbvie: Consultancy, Honoraria, Other: Participation in educational events; Genmab: Consultancy. Shipp:Celgene: Honoraria; Ono Pharmaceutical: Honoraria; Bayer: Honoraria; Bristol Myers Squibb: Consultancy, Research Funding; Merck: Research Funding. Thompson:Merck Sharp & Dohme Corp.: Current Employment. Orlowski:Merck Sharp & Dohme Corp.: Current Employment. Marinello:Merck & Co., Inc., Kenilworth, NJ, USA: Other: Stock ownership; Merck & Co., Inc.: Other: Travel, accommodations, expenses; Merck Sharp & Dohme Corp., a subsidiary of Merck & Co., Inc., Kenilworth, NJ, USA: Current Employment. Armand:Pfizer: Consultancy; Merck & Co., Inc.: Consultancy, Honoraria, Research Funding; Adaptive: Consultancy, Research Funding; Affimed: Consultancy, Research Funding; Sigma Tau: Research Funding; Celgene: Consultancy; IGM: Research Funding; Otsuka: Research Funding; Tensha: Research Funding; Genentech: Research Funding; Infinity: Consultancy; ADC Therapeutics: Consultancy; Bristol-Myers Squibb: Consultancy, Honoraria, Research Funding; Roche: Research Funding.