Can Immune Checkpoint Inhibitors Induce Microscopic Colitis or a Brand New Entity?

Microscopic colitis (MC) has been described as 1 pattern of injury in immune checkpoint inhibitor (ICPI)induced colitis. The main objective of this study was to characterize ICPI-induced MC by exploring the differences in risk factors, colitis treatments, endoscopic features, and clinical outcomes between cancer and noncancer patients with MC with and without exposure to ICPIs. A retrospective chart review was conducted among patients diagnosed with MC from our institutional pathology database from January 2012 to January 2018. Patients were categorized into MC in cancer patients with or without ICPI exposure and in noncancer patients. Risk factors (use of tobacco and certain medications), colitis treatments (antidiarrheals and immunosuppressants), endoscopic features (with or without mucosal abnormality), and clinical outcomes (diarrhea recurrence, hospitalization, mortality) were collected and compared among the 3 groups. Of the 65 eligible patients with MC, 15 cancer patients had exposure to ICPI, 39 cancer patients had no exposure to ICPI, and 11 had no cancer diagnosis. Among the risk factors, proton pump inhibitor was more frequently used in the ICPI-induced MC cohort (P = 0.040). Furthermore, in this population, mucosal abnormality was the most common endoscopic feature compared with normal findings in the non-ICPI-induced MC groups (P = 0.106). Patients with ICPI-induced MC required more treatments with oral and intravenous steroids and nonsteroidal immunosuppressive agents (all P < 0.001) and had a higher rate of hospitalization (P < 0.001). This study suggests that despite some similarities between MC with and without exposure to ICPIs, ICPI-induced MC has a more aggressive disease course that requires more potent immunosuppressive treatment regimens and greater need for hospitalization.