Dostarlimab, an anti‐programmed death‐1 monoclonal antibody, does not cause QT prolongation in patients with solid tumours: A concentration‐QT analysis.

Aims: Patients with solid tumours were treated with the anti‐PD‐1 antibody dostarlimab in the Phase I GARNET trial. This study aimed to examine dostarlimab's effect on corrected QT (QTc) interval and the systemic concentration–QTc interval relationship. Methods: In GARNET Part 2B, patients received 500 mg dostarlimab every 3 weeks (Q3W) for four cycles, then 1000 mg Q6W. Triplicate 12‐lead ECGs were recorded and time‐matched pharmacokinetic (PK) samples collected at screening, on Day 1 of Cycles 1, 4, 5, 8, 12 (pre‐dose and 0.5 h after infusion end), and at treatment end. Concentration–change from baseline QTcF (ΔQTcF) analysis using a linear mixed effects model, summary statistics, incidence of clinically noteworthy ECG values and rhythm abnormalities were evaluated. Results: A total of 377 patients were considered for evaluation (n = 15 excluded from concentration–ΔQTcF). There was a non‐significant concentration–ΔQTcF relationship (0.001589 ms/μg/mL; P =.5906). Mean ΔQTcF increase was <6 ms (upper‐bound two‐sided 90% confidence interval [CI], <10 ms at all post‐dose timepoints). Highest geometric mean concentration was 414.1 μg/mL (Cycle 5 Day 1, 0.5 h) with predicted mean ∆QTcF of 3.064 ms (upper‐bound two‐sided 90% CI: 5.071). Mean QTcF prolongation (all concentrations) was 2.4 ms. QTcF prolongation ≥500 ms occurred in five patients (1.3%); 51 (13.6%) and nine patients (2.4%) had ΔQTcF ≥30 ms and ≥60 ms, respectively. Ten patients (2.7%) reported rhythm abnormalities. No U‐wave abnormalities, torsades de pointes, ventricular tachycardia or ventricular fibrillation/flutter were observed. Conclusions: Dostarlimab does not cause clinically significant QTcF prolongation exceeding the regulatory concern threshold. [ABSTRACT FROM AUTHOR]