ATROPOS is an international, registry-based observational study of cancer patients with immune checkpoint inhibitor-associated myocarditis (ICI-M). The study evaluates whether immunosuppressive treatment strategies, including first-line glucocorticoids and subsequent second-line immunosuppressants, are associated with overall mortality, and whether these associations vary according to myocarditis severity. The target number of cases to be included is 1500 spanning from at least 160 centers, located in at least 18 countries. Analyses will adjust for clinically relevant confounders and may use time-dependent survival models where appropriate.

"ATROPOS (Assessing lethaliTy and Risk factOrs in immune checkPoint inhibitors-induced myOcardia survival analysis based on an international registry) is an observational, non-interventional analysis of the international REDCap registry of immune checkpoint inhibitor-associated myocarditis (ICI-M).

The study population consists of cancer patients exposed to immune checkpoint inhibitors and recorded in the registry with possible, probable, or definite ICI-M according to registry/adjudication definitions. The main objective is to evaluate associations between immunosuppressive treatment strategies and overall mortality, as a function of myocarditis severity, focusing on first-line glucocorticoids and the subsequent use of second-line immunosuppressants. The study will also assess whether these associations are modified by myocarditis severity. Secondary analyses will examine mortality at 30, 90 and 360 days, cause-specific death (e.g. myotoxicity, cancer-related) where available, and clinical risk factors related to oncology history, ICI exposure, symptoms, ECG, echocardiography, cardiac MRI, biomarkers including CK and troponin, other immune-related adverse events, heart failure, respiratory muscle failure, arrhythmias and conductive disorders, sepsis, and pharmacological treatments.

The statistical approach will include descriptive analyses and Cox proportional-hazards modelling. Time-dependent covariates will be considered for variables such as troponin, left ventricular ejection fraction, severity/grade of the myocarditis/myotoxicity, glucocorticoids and other immunosuppressants. Missing data will be described and handled through prespecified methods, with MICE and JointAI used to cross-check robustness of results. Because treatment strategies are not assigned by the protocol, all treatment-effect analyses will be interpreted as observational associations, adjusted for prespecified clinical confounders.

ATROPOS does not assign study treatment, change patient management, require extra visits, or involve a study drug/device. The central analysis dataset uses coded or pseudonymised data, with direct identifiers retained only by local sites when applicable under their own governance."

Inclusion Criteria:

• cancer patients exposed to at least one immune checkpoint inhibitor
• possible, probable or definite immune checkpoint inhibitor-associated myocarditis recorded in the international registry according to registry/adjudication definitions
• available index-date/presentation information
• available mortality follow-up.

Exclusion Criteria:

• duplicate records
• not enough data to classify as myocarditis
• record/patient withdrawn from research use unresolved data-quality issues preventing inclusion in the final SAP-defined analysis set.

Cancer patients exposed to immune checkpoint inhibitors and recorded in a REDCap international ICI-Myocarditis registry, including cases with clinical, biomarker, ECG, imaging, treatment, complication and mortality/outcome data sufficient for the planned survival analyses.