Immune checkpoint inhibitor (ICI) therapy has revolutionized cancer care but is associated with immune-related adverse events (irAEs). Recent case reports raised the concern that acute appendicitis may be an irAE. In this study, we sought to describe the disease course of post-ICI therapy appendicitis and its associated complications. MethodsAdult patients who had an International Classi cation of Diseases code for appendicitis within the rst 2 years after initiating ICI therapy from January 2010 to April 2021 and who had imaging evidence of appendicitis were studied retrospectively. Results13,991 patients were identi ed who had ICI exposure during the study period, 44 had codes for appendicitis, 10 of whom met the inclusion criteria. Their median age at the time of diagnosis was 59 years. The median time from ICI therapy initiation to appendicitis onset was 188 days. The most common presenting symptoms were abdominal pain (70%) and fever (40%).Abscesses were present in two patients, and a perforation was present in one. All 10 patients received broad-spectrum antibiotics. Five patients needed surgery or interventional radiology drainage. Nine patients had resolution of appendicitis symptoms after treatment. ConclusionPost-ICI therapy appendicitis is rare but presents similarly to and has similar complications rates as conventional appendicitis. Appendectomy remains the mainstay of treatment, but its use can be limited in cancer patients. The decision to continue ICI therapy remains at the discretion of the clinician. Further studies are needed to bring awareness to and advance the understanding of this clinical entity.

Figure 1. Radiological features of appendicitis and complications. (A) Contrast-enhanced CT image showing a normal-appearing appendix (arrows, coronal view). (B) Contrast-enhanced CT image showing an appendix perforated by a large, rim-enhancing, partially walled-off collection containing multiple small pockets of air adjacent to the cecum, suggesting an abscess with associated mesentery fat stranding (arrows, coronal view)

PurposeImmune checkpoint inhibitor (ICI) therapy has revolutionized cancer care but is associated with immune-related adverse events (irAEs). Recent case reports raised the concern that acute appendicitis may be an irAE. In this study, we sought to describe the disease course of post-ICI therapy appendicitis and its associated complications.Methods Adult patients who had an International Classification of Diseases code for appendicitis within the first 2 years after initiating ICI therapy from January 2010 to April 2021 and who had imaging evidence of appendicitis were studied retrospectively. Results 13,991 patients were identified who had ICI exposure during the study period, 44 had codes for appendicitis, 10 of whom met the inclusion criteria. Their median age at the time of diagnosis was 59 years. The median time from ICI therapy initiation to appendicitis onset was 188 days. The most common presenting symptoms were abdominal pain (70%) and fever (40%). Abscesses were present in two patients, and a perforation was present in one. All 10 patients received broad-spectrum antibiotics. Five patients needed surgery or interventional radiology drainage. Nine patients had resolution of appendicitis symptoms after treatment. ConclusionPost-ICI therapy appendicitis is rare but presents similarly to and has similar complications rates as conventional appendicitis. Appendectomy remains the mainstay of treatment, but its use can be limited in cancer patients. The decision to continue ICI therapy remains at the discretion of the clinician. Further studies are needed to bring awareness to and advance the understanding of this clinical entity.