On June 13, 2018, the US Food and Drug Administration (FDA) granted accelerated approval to pembrolizumab (Keytruda, Merck) for the treatment of adult and pediatric patients with refractory primary mediastinal large B-cell lymphoma (PMBCL), or who have relapsed after two or more prior lines of therapy.

Approval was based on data from 53 patients with relapsed or refractory PMBCL enrolled in a multicenter, open-label, single-arm trial, KEYNOTE-170 (NCT02576990). Patients were treated with pembrolizumab 200 mg IV every 3 weeks until unacceptable toxicity or documented disease progression, or for up to 24 months for patients who did not progress. The overall response rate was 45% (95% CI: 32, 60), including 11% complete responses and 34% partial responses. The median duration of response was not reached within the follow-up period (median 9.7 months). The median time to first objective response was 2.8 months; pembrolizumab is not recommended for treatment of patients with PMBCL who require urgent cytoreductive therapy.

The most common adverse reactions in ≥10% of patients with PMBCL treated in KEYNOTE-170 were musculoskeletal pain, upper respiratory tract infection, pyrexia, fatigue, cough, dyspnea, diarrhea, abdominal pain, nausea, arrhythmia, and headache. Pembrolizumab was discontinued or interrupted due to adverse reactions in 8% and 15% of patients, respectively. Twenty-five percent of patients had an adverse reaction requiring systemic corticosteroid therapy. Serious adverse reactions occurred in 26% of patients.

The recommended pembrolizumab dose for treatment of adults with PMBCL is 200 mg every 3 weeks. The recommended dose in pediatric patients is 2 mg/kg (up to a maximum of 200 mg) every 3 weeks.

FDA granted this application priority review. Pembrolizumab also received orphan product designation and breakthrough therapy designation for the PMBCL indication. This indication is approved under accelerated approval based on tumor response rate and durability of response. Continued approval for this indication may be contingent upon verification and description of clinical benefit in confirmatory trials.