First-In-Human Study of Cemiplimab Alone or in Combination with Radiotherapy and/or Low-dose Cyclophosphamide in Patients with Advanced Malignancies

Purpose: This first-in-human study assessed the safety, tolerability, dose-limiting toxicities (DLT), antitumor activity, and pharmacokinetics of cemiplimab, a monoclonal anti-programmed cell death-1 (PD-1), as monotherapy and in combination with hypofractionated radiotherapy (hfRT) and/or cyclophosphamide (CPA) in patients with advanced solid tumors. Patients and Methods: Patients were enrolled in 1 of 10 dose escalation cohorts and received cemiplimab 1, 3, or 10 mg/kg every 2 weeks intravenously for up to 48 weeks. Depending on the cohort, patients received hfRT and/or low-dose (200 mg/m²) CPA. Safety was evaluated. Antitumor activity was assessed by Response Evaluation Criteria in Solid Tumors version 1.1. Results: Sixty patients were enrolled. The median duration of follow-up was 19.3 weeks (range, 2.3-84.3). There were no DLTs. The most common treatment-emergent adverse events (TEAEs) of any grade were fatigue (45.0%), nausea (36.7%), and vomiting (25.0%). The most common immune-related adverse events (irAEs) of any grade were arthralgia (10.0%), hypothyroidism (8.3%), and maculopapular rash (8.3%). Cemiplimab pharmacokinetic parameters increased in a close to dose-proportional manner and were similar regardless of combination therapy regimen. Two patients (one with cutaneous squamous cell carcinoma and one with cervical cancer) experienced a complete response; 7 had a partial response. Observed duration of response was ≽12 months in 6 patients. Conclusions: The safety profile of cemiplimab was comparable with other anti-PD-1 agents. Addition of hfRT and/or CPA did not appear to increase grade ≽3 irAEs, suggesting that cemiplimab can be safely administered with hfRT and/or CPA. Cemiplimab exhibited encouraging antitumor activity with 2 complete responses and 7 partial responses observed; responses were also durable.