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T cells play a critical role in immune responses against neoplasm. This finding contributed to the immunotherapy development, an effective treatment for many cancers nowadays. Programmed cell death protein 1 (PD1) is an inhibitory receptor on T cells which downregulate T-cell function per ligation with its ligands (PDL1 and PDL2). PD1 blockade is used to enhance antitumor immunity. Pembrolizumab is a humanized monoclonal anti-PD1 antibody currently used in the management of melanoma, non-small-cell lung cancer, and Hodgkin lymphoma. Most of the treatment toxicities are immune-related adverse events, but grade 3–4 toxicities occur in up to 5% of patients, mainly dermatologic. We present a case of grade 4 pembrolizumab-induced liver toxicity associated with an excellent treatment response in a Caucasian woman.