Checkpoint inhibitor colitis (CIC) is considered to be the most severe adverse effect for patients on immune checkpoint inhibitor (ICI) medications and is the most common cause for discontinuing immunotherapy. However, there is a scarcity in the literature on its investigations and management.

All patients at a large district general hospital receiving ICI medications were screened between 01/01/24 – 31/12/24 for CIC. Baseline demographics, cancer diagnosis, and gastroenterology investigations and treatment variables were collected. A p-value <0.05 was considered statistically significant.

Of 424 patients that received ICI medications, 67 (16%) patients with CIC were identified. The median time from ICI to CIC was 88 days (IQR 59-214). The most common immunotherapy treatment were phosphodiesterase-1 inhibitors (49.3%).

Cancer treatment common adverse events (CTCAE) grades 1-3 for colitis was 48.2%, 16.1% and 35.7%, respectively. Thirty-two patients (48%) required treatment with steroids, whilst the remainder settled with supportive measures only. In patients with grade 3 colitis, 90% required steroid treatment compared to 11.1% with grade 1 (p<0.001). Of patients requiring steroids, 19% required biologic treatment, all of whom were CTCAE grade 3 for colitis (p=0.001). Twenty-three (34%) patients underwent endoscopic evaluation. Erythema was the most common endoscopic finding in 57% of patients, with 42% requiring biologics compared to 0% without erythema (p=0.027). Histologically, 9 patients had acute inflammation, 6 increased apoptosis and 6 crypt distortion with other features including collagenous colitis seen less commonly. Increased apoptosis was associated with the most significant risk factor for requiring biologics (50% versus 11.8% without, p=0.051).

Our data demonstrates that patients with CTCAE grade £ 2 settles either spontaneously or with steroid treatment. Endoscopic findings of erythema and histological findings of increased apoptosis were associated with the need for biologic initiation. Further work is needed to explore treatment efficacy and treatment prophylaxis.