Safety & tolerability of pembrolizumab in patients with relapsed/refractory primary mediastinal large B-cell lymphoma

Treatment options for relapsed/refractory primary mediastinal large B-cell lymphoma (rrPMBCL) are limited and prognosis is generally poor (overall response rate [ORR] 0-25%; 2-year overall survival 15%). PMBCL frequently involves PD-1 ligand overexpression, potentially making PMBCL particularly susceptible to PD-1 blockade. We evaluated safety and antitumor activity of pembrolizumab, an anti-PD-1 antibody, in rrPMBCL as part of the KEYNOTE-013 multicohort Phase 1b trial. At time of data cutoff, 18 patients (median age 30; median 3 prior lines of therapy) had been enrolled and treated, of whom 17 were included in the efficacy analyses. Eleven patients (61%) experienced drug-related adverse events, mostly grade 1-2; none discontinued treatment due to adverse events. ORR was 41% (7/17); 6 additional patients (35%) had stable disease. Of patients evaluable by imaging, 13/16 (81%) had decreases in target lesions. With a median follow-up of 11.3 months, median duration of response was not reached. Two patients reached the maximum 2-year treatment duration and remain in remission. Median overall survival was not reached for treated patients overall; all responders were still alive at data cutoff. These results in heavily pretreated rrPMBCL patients demonstrate that PD-1 blockade with pembrolizumab has a manageable safety profile and promising antitumor activity. (Registered to www.clinicaltrials.gov as NCT01953692).