Menna-Allah Elaskandrany, DO1, Mohamed Ismail, DO2, Mahinaz Mohsen, MD2, Muhammad Hassaan Arif Maan, MBBS2, Michael Bebawy, DO2, Sameer Rao, MBBS2, Michael Farber, DO3, Weizheng Wang, MD2 1Lenox Hill Hospital, Northwell Health, New York, NY; 2Rutgers New Jersey Medical School, Newark, NJ; 3New York Institute of Technology College of Osteopathic Medicine, Glen Head, NY Introduction: Immune checkpoint inhibitors (ICIs) have revolutionized cancer therapy due to their ability to enhance the immune system’s recognition and destruction of cancer cells. While these medications have been utilized in the treatment of multiple malignancies including non-small cell lung cancer (NSCLC) and melanoma, they can also trigger immune-mediated adverse events such as endocrinopathies, pneumonitis, and colitis. ICI-induced colitis, a rare adverse event, occurs 6-8 weeks after initiation of therapy, although there have been cases of delayed presentations. The presentation includes watery diarrhea, abdominal pain, rectal bleeding, or colonic perforation. In order to make the diagnosis of ICI-induced colitis, colonoscopy is performed to detect the presence of colitis.
Case Description/
Methods: A 76 year old male with stage IV NSCLC presented to the ED in May 2025 with abdominal pain and a three week history of watery, non bloody diarrhea. He denied recent travel, hospitalizations, dietary changes, or sick contacts. He was started on pembrolizumab December 2024 and had received his last infusion two weeks prior to the onset of his symptoms. His outpatient oncologist started him on prednisone 50mg once daily, but eventually presented to the ED after his symptoms failed to resolve. On admission, GI PCR and clostridium difficile testing were negative, and CT abdomen and pelvis showed wall thickening of the left hemicolon and ascending colon, suspicious for colitis. Fecal calprotectin was 3600 mcg/g, indicating inflammation. The patient was started on methylprednisolone 120 mg IV daily, and after 5 days, his symptoms improved. Colonoscopy showed evidence of mayo grade 2 colitis, while biopsies of the cecum, transverse, descending, and sigmoid colons showed evidence of active colitis, confirming the diagnosis of ICI-induced colitis. The patient was switched to prednisone with plans to follow up with his oncologist to further taper the steroids. Discussion: This case highlights the presentation, evaluation, and therapeutic approach to a rare ICI-associated adverse event. The rapid response to high-dose corticosteroids supports the current guidelines of using corticosteroids in moderate to severe cases of ICI-induced colitis. This case highlights the utility of promptly identifying ICI-induced colitis and the need for multidisciplinary coordination in the management of such cases to prevent long-term oncologic or gastrointestinal complications, while also balancing the patient’s cancer treatment goals.
Disclosures: Menna-Allah Elaskandrany indicated no relevant financial relationships. Mohamed Ismail indicated no relevant financial relationships. Mahinaz Mohsen indicated no relevant financial relationships. Muhammad Hassaan Arif Maan indicated no relevant financial relationships. Michael Bebawy indicated no relevant financial relationships. Sameer Rao indicated no relevant financial relationships. Michael Farber indicated no relevant financial relationships. Weizheng Wang indicated no relevant financial relationships.
Menna-Allah Elaskandrany, DO1, Mohamed Ismail, DO2, Mahinaz Mohsen, MD2, Muhammad Hassaan Arif Maan, MBBS2, Michael Bebawy, DO2, Sameer Rao, MBBS2, Michael Farber, DO3, Weizheng Wang, MD2. P3411 - Pembrolizumab-Induced Immune Checkpoint Inhibitor Colitis, ACG 2025 Annual Scientific Meeting Abstracts. Phoenix, AZ: American College of Gastroenterology.
