Myocardial Expression of PD-L1 as a Marker of Poor Prognosis in Immune Checkpoint Inhibitor–Associated Myocarditis

BACKGROUND: Immune checkpoint inhibitors (ICIs) have improved cancer outcomes but are associated with severe immune-related adverse events, including myocarditis. PD-L1 plays an important role in immune regulation and homeostasis. Myocardial PD-L1 up-regulation has been reported in ICI-associated myocarditis; however, its clinical significance and prognostic value remain unclear. OBJECTIVES: This study sought to investigate the association between myocardial PD-L1 expression and ICI-associated myocarditis severity and prognosis. METHODS: Twenty consecutive cases of biopsy-proven ICI-associated myocarditis were analyzed. Endomyocardial biopsy specimens underwent immunohistochemical staining for PD-L1, and patients were categorized into high (≥8%) or low (<8%) PD-L1 expression groups. Clinical presentation and the incidence of major adverse cardiotoxic events, defined as a composite of severe heart failure, severe arrhythmia, or cardiac death, were compared between groups. RESULTS: macrophage infiltration (15.2% [Q1-Q3: 10.2%-21.1%] vs 1.23% [Q1-Q3: 0.4%-2.3%]; P = 0.007). CONCLUSIONS: High myocardial PD-L1 expression is associated with greater disease severity and a higher risk of major adverse cardiotoxic events in ICI-associated myocarditis. Assessment of PD-L1 expression in endomyocardial biopsy specimens may help identify patients at high risk who may benefit from early intervention and closer monitoring.