Diagnosing Immune Checkpoint Inhibitor-Induced Myocarditis: Insights, Challenges, and Uncertainties

Recent advancements in immunotherapy have substantially improved overall survival and quality of life among patients with cancer. Notably, immune checkpoint inhibitors (ICIs) have emerged as a revolutionary strategy, particularly in the management of advanced cancers. However, the success of ICIs is accompanied by the challenge of immune-related adverse events. Although rare, cardiovascular adverse events associated with ICIs are associated with high fatality rates and rapid clinical progression, thereby necessitating timely intervention. This review explores the histopathologic characteristics of ICI-induced myocarditis, shedding light on the complexities of diagnosis and management. Several studies examining the histopathologic features of ICI-induced myocarditis have emphasized the roles of macrophages and the potential utility of ancillary tests such as immunohistochemistry. Quantifying CD68+ macrophage abundance may enhance diagnostic sensitivity, thereby providing valuable insights into clinical outcomes. In conclusion, this review underscores the need for a nuanced approach to diagnosing ICI-induced myocarditis. The comprehensive exploration of histopathologic characteristics, ancillary tests, and emerging diagnostic markers provides valuable guidance for practicing pathologists. As the population of ICI-treated patients with cancer continues to grow, optimizing immunohistochemistry panels and refining diagnostic criteria will be crucial to address the unique challenges posed by ICI-induced myocarditis.