Myocarditis in Patients Starting Combination Checkpoint Inhibitor Therapy: Analysis of a Commercial Claims Database

Background Immune checkpoint inhibitors have improved the clinical outcomes of several cancers but have also been associated with a greater risk of immune-related adverse effects, especially when combined. The objective of this study was to investigate the incidence of myocarditis in relation to the use of dual concurrent versus single immune checkpoint inhibitors therapies.Methods and Results A cohort study was conducted using medical and pharmacy claims data (2011-2022) from a large US commercial insurer. Cox regression quantified the comparative risks of myocarditis or heart failure in patients with cancer receiving treatment with combination therapy (nivolumab and ipilimumab) in comparison to taking a single immune checkpoint inhibitor only. Mean follow-up time in 53 018 patients was 226 days (interquartile range, 93-495 days). There were 148 cases of myocarditis (0.3%), 33 (0.7%) in patients on combination therapy, and 115 (0.2%) in patients on monotherapy. The risk of myocarditis per 1000 patients was 7.40 in the combination therapy group and 2.37 in the monotherapy group (risk ratio, 3.12 [95% CI, 2.12-4.60]). Using multivariable regression analysis, the hazard ratio for myocarditis in the combination therapy group was 2.38 (1.57-3.63). No difference in the risk of heart failure was found between combination and single therapy.Conclusions Therapy with 2 immune checkpoint inhibitors was associated with an increased risk of myocarditis compared with monotherapy, with most cases occurring in the first 6 months of therapy.