Pembrolizumab should be permanently discontinued if the patient has a severe (grade 4) adverse reaction, including infusion-related reactions, pneumonitis, nephritis, or aspartate aminotransferase (AST) or alanine aminotransferase (ALT) levels greater than five times the upper limit of normal (ULN), total bilirubin greater than three times ULN, failure of the adverse reaction to return to grade 0 or 1, recurrence of a grade 3 or higher event, or failure to taper steroids within 12 weeks of initiation (Merck, 2014a). This evidence concerns the gene GPT and pneumonitis.