A Case of Acquired Factor V Inhibitor Following Nivolumab Administration

Acquired factor V inhibitor (AFVI) is a very rare disease. We presented herein a case of hypopharyngeal cancer in which AFVI developed after nivolumab administration. Blood test findings two weeks after the first dose of nivolumab showed a significant prolongation of prothrombin time (PT) and activated partial thromboplastin time (APTT), indicating a marked abnormality in the coagulation function. Factor V activity had decreased significantly and was below the detection limit (<3%), and the factor V inhibitor level was as high as 16 Bethesda units (BU)/mL. His underlying illness was a malignant tumor, but we considered that nivolumab administration was the cause of AFVI, considering the time when coagulation abnormality developed. No significant bleeding tendency was observed in the subsequent course, and the AFVI was followed up without treatment. To the best of our knowledge, the present study is the first to report AFVI occurrence after immune checkpoint inhibitor administration.