Pembrolizumab-induced thrombotic thrombocytopenic purpura.

Acquired thrombotic thrombocytopenic purpura is an autoimmune disorder caused by an inhibitory autoantibody against ADAMTS-13. While most cases of acquired thrombotic thrombocytopenic purpura are idiopathic, certain conditions (e.g. bacterial infection, autoimmune disorders, malignancies) and medications are associated with thrombotic thrombocytopenic purpura. Other potential causes were eliminated in our patient. As acquired thrombotic thrombocytopenic purpura is an autoimmune disorder, pembrolizumab, given its unique mechanism of action and association with immune-related adverse events, is believed to be implicated in the development of thrombotic thrombocytopenic purpura. This case is one of only two linking anti-PD-1 therapy to thrombotic thrombocytopenic purpura development (the other occurring in a patient on nivolumab plus ipilimumab). Thrombotic thrombocytopenic purpura is life-threatening and clinicians are advised to be aware of its possible occurrence in immune checkpoint inhibitor-treated patients.