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Introduction Cancer immunotherapy with immune checkpoint inhibitors (ICIs) has transformed outcomes across multiple tumour types. However, their use is frequently complicated by immune-related adverse events (irAEs), with colitis being one of the most clinically significant gastrointestinal toxicities. Although the British Society of Gastroenterology (BSG) has published guidelines for the management of ICI-induced enterocolitis, immunotherapy-related colitis remains a relatively new clinical entity that presents ongoing challenges in diagnosis, investigation and management. With the expanding use of ICIs in oncology, gastroenterologists are increasingly likely to encounter these cases, highlighting the need for improved recognition and evidence-based treatment approaches.Methods We conducted a single-centre retrospective review of electronic medical records for 214 patients treated with ICIs at University Hospital Coventry between January 2024 and December 2024. Patients received PD-1, PD-L1, CTLA-4 or LAG-3 inhibitors as monotherapy or in combination with VEGF/VEGFR-targeted agents and/or chemotherapy. Immunotherapy-related colitis was identified in 4.67% of the cohort. Detailed data were collected on clinical presentation, investigations, management strategies and outcomes.Results Immunotherapy-related colitis was diagnosed in 4.67% (10/214) of patients ( figrue 1). Most affected patients received ICIs for metastatic melanoma (n=8), with the remaining patients treated for metastatic breast cancer and poorly differentiated squamous cell carcinoma of the mid-oesophagus. All cases occurred during treatment with PD-1 inhibitors. Eight patients received pembrolizumab (six as monotherapy and two in combination with carboplatin plus paclitaxel or oxaliplatin plus capecitabine), while two received combination nivolumab and ipilimumab. None had a prior history of inflammatory bowel disease.All patients presented with diarrhoea (2–8 bowel movements/day). Abdominal pain occurred in five cases and rectal bleeding in one case. Immunotherapy was discontinued in 9 patients. 90% of patients received corticosteroids. Most were initiated on prednisolone 60 mg daily (n=6); however, some received 30 mg (n=1), 40 mg (n=1), or 90 mg (n=1), and some required intravenous methylprednisolone (2 mg/kg). Half of the cohort (50%) demonstrated steroid-refractory disease and required escalation to biologic therapy. All escalated cases were treated with Infliximab (5 mg/kg), receiving 2–5 doses. Clinical response was limited, with partial or absent improvement.All patients underwent endoscopic evaluation (eight flexible sigmoidoscopies, two colonoscopies). Endoscopic findings ranged from mild mucosal erythema to features consistent with colitis. Biopsies demonstrated a spectrum of histopathological changes, including normal mucosa, microscopic colitis, and active to moderately active colitis. Three cases exhibited microscopic patterns (collagenous colitis, lymphocytic colitis and one unspecified).Conclusions Immunotherapy-related colitis represents an emerging clinical challenge within gastroenterology. Our findings highlight variability in clinical presentation, endoscopic and histopathological features, and therapeutic responses. Despite guideline-supported management, gaps remain in predicting disease phenotype, identifying steroid-refractory cases and optimising biologic escalation. Larger multicentre studies are required to characterise this condition further and refine evidence-based management strategies in the context of expanding immuno-oncology practice.Abstract P333 Figure 1