Immune checkpoint inhibitors (nivolumab, pembrolizumab) targeting PD-1 cause immune-related adverse events. The organ most frequently affected in severe immune-related adverse events is:

• A Thyroid gland (hypothyroidism/thyroiditis)
• B Lung (pneumonitis)
• C Colon (immune-mediated colitis) ✓
• D Skin (rash/pruritus)

Explanation

PD-1/PD-L1 inhibitors can cause immune-related adverse events (irAEs) affecting virtually any organ as a consequence of breaking peripheral immune tolerance. While dermatological toxicity (rash, pruritus) is the most common irAE overall (>30% incidence), immune-mediated colitis is the most common severe (grade 3-4) adverse event requiring systemic corticosteroid therapy or drug discontinuation. Colitis presents with diarrhea, abdominal pain, and bloody stool, and can be life-threatening if untreated. Endocrine irAEs (thyroiditis, hypophysitis, adrenalitis) and pneumonitis are also important; pneumonitis, though less frequent, has the highest case fatality rate among irAEs. All irAEs are managed with immunosuppression (corticosteroids first line).

Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.

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Written and medically reviewed by the StethoPrep medical team.