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irAEGIICD-10 K52.x

ICI-related colitis

ICI colitis · checkpoint-inhibitor colitis · immune-mediated diarrhoea / colitis

ICI-related colitis is a common gastrointestinal irAE, affecting 5-15% of patients on anti-PD-1, 25-30% on anti-CTLA-4 (ipilimumab) and up to 40% on combination ICI. Onset is typically 5-10 weeks but can be earlier with anti-CTLA-4 and later with anti-PD-1. Presentations range from mild diarrhoea to severe / perforating colitis. UK BSG and ESMO guidelines underpin management with steroids first-line, infliximab (5 mg/kg) or vedolizumab for steroid-refractory disease.

CurrentLast reviewed 16 May 2026

Epidemiology

  • Incidence (any grade):
    • Anti-PD-1 monotherapy: 5-15%.
    • Anti-CTLA-4 monotherapy (ipilimumab): 25-30%; G3+ 5-10%.
    • Combination ICI: 30-40%; G3+ 10-15%.
  • Onset: anti-CTLA-4 commonly 5-10 weeks; anti-PD-1 can be later (months).
  • Sigmoid colon and rectum most commonly affected; pan-colitis or ileitis less common.

Clinical features

  • Diarrhoea — watery to bloody.
  • Abdominal pain / cramps.
  • Mucus, urgency, tenesmus (rectal involvement).
  • Constitutional: fever, weight loss, fatigue.
  • Red flags / serious:
    • Bloody diarrhoea.
    • Abdominal distension, tenderness.
    • Fever.
    • Toxic megacolon, perforation (G4 emergencies).
  • Differential: Clostridium difficile, CMV, viral / bacterial gastroenteritis, drug-induced (laxatives), tumour metastasis to bowel.

CTCAE grading

GradeSymptomsAction
G1<4 stools/day over baseline; asymptomaticContinue ICI; loperamide; dietary advice.
G24-6 stools/day over baseline; abdominal pain; mucus / bloodHold ICI; budesonide / prednisolone 0.5-1 mg/kg; consider sigmoidoscopy.
G3≥7 stools/day; severe pain; peritoneal signs; hospitalisationHold ICI; admit; IV methylprednisolone 1-2 mg/kg; flexible sigmoidoscopy; infliximab / vedolizumab if refractory.
G4Life-threatening; perforation; toxic megacolonPermanently discontinue ICI; IV methylprednisolone 2 mg/kg; surgical review; biologic.

Workup

  • Detailed history: stool frequency, blood / mucus, abdominal pain, time from ICI start.
  • Examination: abdominal tenderness, peritoneal signs, fever, dehydration.
  • Stool: culture, C. difficile toxin, calprotectin (raised in colitis).
  • Bloods: FBC, CRP, U&E, LFT, albumin, lactate.
  • Imaging: CT abdomen for moderate-severe disease (rule out perforation, megacolon, abscess).
  • Endoscopy: flexible sigmoidoscopy / colonoscopy with biopsy for G2-3 (or where empirical management not improving); confirms diagnosis, severity (Mayo / endoscopic), excludes CMV.
  • CMV PCR on biopsy in steroid-refractory / immunocompromised.
  • HIV testing in atypical / severe / refractory cases.

Management

  • G1: continue ICI; symptomatic — loperamide, fluid replacement, dietary advice (low residue).
  • G2:
    • Hold ICI.
    • Budesonide 9 mg OD if isolated distal colitis; or oral prednisolone 0.5-1 mg/kg/day.
    • Improvement expected in 5-7 days; if not → escalate.
  • G3:
    • Hold ICI; admit.
    • IV methylprednisolone 1-2 mg/kg/day; switch to oral prednisolone with taper once improving.
    • Flexible sigmoidoscopy.
    • If no improvement within 48-72 h → infliximab 5 mg/kg or vedolizumab 300 mg IV.
    • Repeat infliximab at 2 weeks if needed; vedolizumab at 2 weeks, 6 weeks, then 8-weekly.
  • G4:
    • Permanently discontinue ICI.
    • IV methylprednisolone 2 mg/kg/day.
    • Urgent surgical review (perforation / megacolon).
    • Infliximab / vedolizumab; consider tofacitinib in refractory.
  • Steroid taper over 4-8 weeks with PPI / calcium / vitamin D / glycaemic monitoring.
  • ICI rechallenge: case-by-case; consider switch to PD-1 monotherapy in G2 anti-CTLA-4 colitis after recovery.
  • BSG UK guidelines recommend gastroenterology MDT input for G3+.

References

  1. Haanen J et al. ESMO Clinical Practice Guideline for immune-related adverse events. Ann Oncol. 2022;33:1217-1238.
  2. Schneider BJ et al. ASCO clinical practice guideline update: management of immune-related adverse events. J Clin Oncol. 2021;39:4073-4126.
  3. Powell N et al. BSG practice guidelines on the management of acute severe colitis in patients receiving immune-checkpoint inhibitors. Gut. 2020;69:1581-1592.
  4. Bergqvist V et al. Vedolizumab treatment for immune checkpoint inhibitor-induced enterocolitis. Cancer Immunol Immunother. 2017;66:581-592.
  5. NICE TA342. Vedolizumab for treating moderately to severely active ulcerative colitis. London: NICE; 2015.

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