Pathology

Immune checkpoint inhibitors (ICIs) have gained more and more popularity as cancer treatment in recent years. These drugs have broad-spectrum activity and show effectiveness in more than 10 different types of cancers. They usually have favorable toxicity profiles compared to traditional treatment modalities, such as chemotherapy and radiotherapy. However, ICIs are associated with a wide spectrum of organ toxicities termed immune-related adverse events. A timely diagnosis is paramount as early intervention may lead to partial or complete reversion from toxicity, whereas a delayed treatment could result in more severe toxicity, sometimes irreversible organ damage, or even death. Within the appropriate clinical context, a treating physician should maintain a high suspicion index. When appropriate, biopsy samples should be taken to be evaluated by an experienced pathologist. Moreover, clinical–pathological correlation is essential because oftentimes the degrees of clinical toxicity/symptoms are not necessarily matched to pathological findings. In this chapter, we aim to summarize the ICI-associated cytotoxic effects on organ systems from the pathological perspective.