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Taro OSADA2), Shinichi SASAKI3), Takashi YAO4)Akane HASHIZUME1), Hiroshi IZUMI1), Shigeki TOMITA1), 1)Department of Pathology, Juntendo University Urayasu Hospital, Chiba, Japan2)Department of Gastroenterology, Juntendo University Urayasu Hospital, Chiba, Japan4)Department of Human Pathology, Juntendo University Faculty of Medicine, Tokyo, Japan3)Department of Internal Medicine and Respiratory, Juntendo University Urayasu Hospital, Chiba, JapanCorresponding author: Akane HashizumeDepartment of Pathology, Juntendo University Urayasu Hospital2-1-1 Tomioka, Urayasu, Chiba 279-0021, JapanTEL: +81-47-353-3111　E-mail: akane@juntendo-urayasu.jpThis paper was presented at the 91st Meeting of the Japanese Society of Pathology Kanto.〔Received　Feb. 2, 2022〕〔Accepted　Apr. 4, 2022〕J-STAGE Advance published date: Jul. 14, 2022Copyright © 2022 The Juntendo Medical Society. This is an open access article distributed under the terms of Creative Commons Attribution License (CC BY), which permits unrestricted use, distribution, and reproduction in any medium, provided the original source is properly credited. doi: 10.14789/jmj.JMJ22-0004-CR　In this article, we report the case of a patient with unresectable stage III squamous cell lung carcinoma who developed immune-related adverse events in the gastrointestinal tract following the administration of immune checkpoint inhibitors. The patient developed severe acute respiratory syndrome coronavirus 2 pneumonia and cytomegalovirus gastritis during immunosuppressive therapy for an immune-related adverse event. Cytomegalovirus infection was managed with the administration of ganciclovir.Juntendo Medical Journal2022. 68(4), 393-397Key words: immunotherapy, adverse events, colitis, gastritis, cytomegalovirusCase ReportsHistopathologic Features of Immune-related Adverse Events in the Gastrointestinal Tract: A Case of Severe Acute Respiratory Syndrome Coronavirus 2 and Cytomegalovirus Infection in a Patient with Lung Squamous Cell Carcinoma Receiving Immune Checkpoint InhibitorsIntroductionImmune checkpoint inhibitors are commonly used for the treatment of advanced-stage malig-nancies. Despite their chance to achieve long-term efficacy, they may induce immune-related adverse events (irAEs). The main irAEs include endocr-inopathies, hepatitis, interstitial pneumonia, skin lesions, mucosal inflammation, diarrhea, and colitis. Although most irAEs with severe toxicity are managed with immunosuppressive therapies, occa-sionally, they can induce infectious disease (e.g., cytomegalovirus infection). This report presents the case of a patient with lung squamous cell carci-noma (SCC) who developed gastrointestinal irAEs, as well as subsequent severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and cyto-megalovirus infection.A man in his seventies was referred to our hospital following the detection of a nodule in the right lung during a routine health examination. Transbronchial biopsy revealed the presence of SCC. (Figure 1A). The examination for epidermal growth factor receptor (EGFR) mutation, anaplastic lymphoma kinase (ALK) translocation, and ROS1 proto-oncogene receptor tyrosine kinase (ROS1) mutations yielded negative results. The tumor proportion score of programmed cell death 1 ligand 1 (PD-L1) was 95% (Figure 1B). The patient was finally diagnosed with stage IIIA lung SCC, and 393Case report