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Introduction Cancer immunotherapy with immune checkpoint inhibitors (ICIs) has improved oncological outcomes but is linked to immune-related adverse events (irAEs). Cardiac irAEs, particularly myocarditis, are associated with high mortality and often require discontinuation of immunotherapy, which is a major concern. ICI-related myocarditis often presents with non-specific symptoms and minimal echocardiography findings, posing a diagnostic challenge. A better understanding of this condition and its association with cardiac biomarkers is crucial for early recognition and reducing associated mortality.Purpose The aim of this analysis was to retrospectively evaluate the utility of measuring N-terminal pro B-type natriuretic peptide (NT-proBNP) compared with Troponin T (cTnT) on presentation in patients diagnosed with ICI-related myocarditis and serially while receiving immunosuppression.Methods This retrospective single-center observational study evaluated cases of ICI-related myocarditis over 12 months. To minimise potential confounders affecting biomarkers, cases associated with concurrent acute coronary syndrome or tachyarrhythmias were excluded. The collected and analysed data included: (i) patient demographics, (ii) baseline NT-proBNP and cTnT levels, (iii) presenting NT-proBNP and cTnT levels, and (iv) seven serial measurements of NT-proBNP and cTnT after initiating corticosteroid therapy. Baseline values were missing for three patients and were imputated using median values. Thereafter, the percentage increase relative to baseline in presenting NT-proBNP and cTnT levels were calculated and assessed using the Wilcoxon signed-rank test. Serial NT-proBNP and cTnT levels after treatment initiation were compared following standardisation with Z-score.Results Out of 58 patients that were evaluated, 16 cases of ICI-related myocarditis were included in our analysis. The plasma levels of NT-proBNP on initial presentation with myocarditis ranged from 571 to 16958 pg/mL (median 2043 pg/mL, IQR 4276), whilst cTnT ranged 11 to 176 ng/L (median 41 ng/L, IQR 47.5). Following imputation for missing baseline biomarker values, a mean percentage increase from baseline biomarkers on presentation for NT-proBNP was 2105% ( p = < 0.001), whereas for cTnT was 305% (p = < 0.001) (figure 1). NT-proBNP showed a serial decrease with immunosuppression, however this was not observed for cTnT which showed a fluctuation (figure 2).Abstract 1-011 Figure 1Percentage increase in cardiac biomarkers cTnT and NT-proBNP from respective baselineAbstract 1-011 Figure 2Serial measurement of cardiac biomarkers cTnT and NT-proBNP to assess therapy responseConclusion In our dataset, NT-proBNP is more significantly elevated over baseline in ICI-related myocarditis compared to cTnT. Serial NT-proBNP measurements were useful in assessing response to steroid therapy. These two observations suggest that NT-proBNP may be a more effective biomarker than cTnT in ICI myocarditis. However, NT-proBNP is non-specific and should be used alongside imaging, with diagnostic and management decisions made in consultation with specialists.