Dose exploration results from Phase 1 study of cemiplimab, a human monoclonal programmed death (PD)-1 antibody, in Japanese patients with advanced malignancies.

Purpose: Part 1 of this two-part, open-label, Phase 1 study (NCT03233139) assessed the safety, tolerability, pharmacokinetics, immunogenicity, and clinical activity of cemiplimab in Japanese patients with advanced malignancies.

Methods: Patients received cemiplimab 250 mg (n = 6) or 350 mg (n = 7) every 3 weeks intravenously for up to 108 weeks in Part 1. Tumor responses were assessed by investigators every 9 weeks using the Response Evaluation Criteria in Solid Tumors version 1.1.

Results: Of 13 patients enrolled, median age was 62 years (range 33-75) and eight patients were female. Median duration of cemiplimab exposure was 13.1 weeks (range 3.0‒113.6). At the time of data cut-off, 11 patients (84.6%) had discontinued treatment (majority due to disease progression: n = 8, 61.5%). The most common treatment-emergent adverse events (TEAEs) of any grade were contact dermatitis, rash, and viral upper respiratory tract infection (each n = 3, 23.1%). Five grade ≥ 3 TEAEs were reported in four patients: autoimmune colitis, dehydration, hyponatremia, hypophosphatemia, and muscular weakness. No dose-limiting toxicities were reported and no TEAEs led to death. Cemiplimab concentrations in serum were consistent with previously reported pharmacokinetic characteristics of cemiplimab. No anti-drug antibodies were detected in serum. Objective response rate [ORR; complete response + partial response (PR)] was 30.8% (four PR) and disease control rate [ORR + stable disease (SD)] was 46.2% (6/13; two SD).

Conclusion: Cemiplimab exhibited antitumor activity in Japanese patients with advanced malignancies. The safety profile was comparable to those previously reported for cemiplimab and other PD-1 inhibitors.

Trial Registration: NCT03233139 at ClinicalTrials.gov.