CaseAdvanced · irAE
Grade 3 colitis on adjuvant pembrolizumab
A 60-year-old man on month 5 of adjuvant pembrolizumab for resected stage IIIB melanoma develops worsening watery diarrhoea (10+ stools/day).
Diagnosis
Grade 3 immune-related colitis on anti-PD-1 monotherapy — hold ICI, methylprednisolone, infliximab if refractory
Learning points
- irAE colitis is one of the most common serious anti-PD-1 / anti-CTLA-4 toxicities. Combination ipi/nivo has the highest rate; anti-PD-1 monotherapy lower but still significant.
- CTCAE grading drives management: G1 (<4 stools/day above baseline, no alarm symptoms) — usually continue ICI with close monitoring; G2 (4–6 stools/day, abdominal pain, blood/mucus) — hold ICI, oral prednisolone around 1 mg/kg/day where steroids are indicated; G3 (≥7 stools/day, severe pain, peritoneal signs or admission indicated) — hold ICI, admit and give IV methylprednisolone 1–2 mg/kg/day; G4 (life-threatening) — permanent discontinuation.
- Always exclude infection (stool C. diff, Salmonella, Shigella, Campylobacter, CMV in steroid-refractory cases) before assuming irAE.
- Steroid-refractory irAE colitis (no improvement in 3–5 days): add infliximab 5 mg/kg OR vedolizumab. Repeat at 2 weeks if needed.
- ICI generally permanently discontinued after grade 3+ colitis; consult MDT for selected cases where rechallenge after full resolution and steroid taper is considered.
- Endocrine irAEs (thyroiditis, hypophysitis) often allow continued ICI with hormone replacement — distinct from GI / hepatic / pulmonary irAEs which usually require ICI hold ± permanent discontinuation.