Enzalutamide‐induced severe thrombocytopenia complicated by a seizure in a 76‐year‐old man with castration‐resistant prostate cancer

Introduction Adverse events with enzalutamide widely used for men with castration‐resistant prostate cancer are of interest. Case presentation A 76‐year‐old man developed castration‐resistant prostate cancer. He received 160 mg of enzalutamide daily. On the 13th day after treatment, severe thrombocytopenia was observed (platelet count: 1.9 × 104/μL). Normal coagulation and fibrinolytic systems suggested thrombocytopenia induced by enzalutamide. Enzalutamide was withdrawn immediately, and platelet count uneventfully recovered to 7.0 × 104/μL and 28.8 × 104/μL 9 and 30 days after discontinuation, respectively. He restarted enzalutamide therapy without thrombocytopenia recurrence. However, 81 days after restarting enzalutamide, he experienced a seizure. There were no significant findings from brain computed tomography, which suggested that the seizure was also an enzalutamide‐associated adverse event. Conclusion Thrombocytopenia may occur early following enzalutamide therapy, and blood analysis within 2 weeks after treatment may facilitate its management. Enzalutamide‐induced thrombocytopenia, complicated by seizure, has not been reported.