Frequency and Consequences of Immune Checkpoint Inhibitor–Associated Inflammatory Changes in Different Organs: An Autopsy Study Over 13 -Years

Although immune checkpoint inhibitors (ICIs) have revolutionized modern oncology, they are also associated with immune-related adverse events (irAEs). Previous histopathologic descriptions of organ-related inflammatory changes do not consider systemic effects of ICIs, because of the absence of comprehensive autopsy studies. We performed a retrospective study on 42 whole-body autopsies of patients treated with ICIs from January 2011 to March 2024 to determine the frequency, organ distribution, and morphology of ICI-associated inflammatory changes as well as their clinical relevance. Twenty-three of 42 (54.8%) patients presented irAEs with inflammatory changes in at least one organ. Most frequent irAEs were ICI-related hypophysitis (N = 12; 28.6%), myocarditis (N = 8; 19.0%), pneumonitis (N = 5; 11.9%), hepatitis (N = 6; 14.3%), and adrenalitis (N = 5; 11.9%). ICI-related inflammation was mainly characterized by lymphohistiocytic and macrophage-rich tissue infiltrates, whereas a granulomatous "sarcoid-like" reaction was observed in 1 patient. Cause of death was attributable to ICI therapy in 7 (16.7%) patients, with ICI-associated myocarditis as the most common cause of death (N = 5; 71.4%). Clinically, irAEs were unsuspected in 5 of 7 ICI-related deaths (71.4%). Among irAEs, myocarditis has been clinically undiagnosed in 5 out of 8 cases (62.5%). Encephalitis was identified only at autopsy in all cases (N = 2). Hypophysitis was clinically unsuspected in 8 of 12 (66.7%) cases. Patients who died from irAEs developed more frequently a complete tumor regression than patients who died from other causes (P = .018). Of note, ICI-related myocarditis and pneumonitis were both associated with a systemic occurrence irAEs. Our study demonstrates that some irAEs, especially myocarditis, hypophysitis, and encephalitis, are clinically underdiagnosed. Autopsy remains a valuable tool to monitor diagnostic accuracy and therapeutic side effects in patients who died under ICI therapy.