The patient developed delayed severe hepatitis at 15 months after initiating pembrolizumab treatment, presenting "Grade 4 aspartate aminotransferase increase" and "Grade 4 alanine aminotransferase increase." Impaired liver function persisted despite pulse corticosteroid therapy with intravenous methylprednisolone 1,000 mg/day, followed by oral prednisolone 2 mg/kg/day and oral mycophenolate mofetil 2,000 mg/day. Here, GPT is linked to Hepatitis.