A patient completed nivolumab for metastatic melanoma 4 months ago. She now presents with new-onset watery diarrhea (6 stools/day) and abdominal pain. Colonoscopy shows patchy colitis with ulcerations. Which statement about this presentation is correct?

• A Immune-related adverse events cannot occur after drug discontinuation; this is likely infectious colitis
• B Nivolumab has a short half-life, so irAEs are impossible after 2 weeks of discontinuation
• C Diarrhea occurring beyond 12 weeks from last dose is never immune-related
• D Immune checkpoint inhibitor colitis can present weeks to months after the last dose and should be managed as an irAE ✓

Explanation

Immune-related adverse events from checkpoint inhibitors can present weeks to months after the last dose due to persistent immune activation. Nivolumab's half-life is approximately 25 days, but the immune dysregulation persists. Onset of colitis 4 months after completion is well-documented. Infectious causes should be excluded, but irAE remains the primary consideration.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

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