Prostate cancer-associated Trousseau's syndrome presenting as stroke in a 42-year-old man.

We report a 42-year-old man presenting with acute left hemiparesis and multiple cerebral infarctions accompanied by markedly elevated D-dimer levels, suggesting cancer-associated thrombosis without an identifiable primary malignancy. Six months later, he was diagnosed with advanced prostate adenocarcinoma with multiple bone metastases and a markedly elevated prostate-specific antigen level. Treatment with apalutamide and degarelix was initiated. Despite early recurrent thromboembolic events, PSA and D-dimer levels gradually decreased. At 10 months, both markers were significantly reduced and no further thrombosis occurred. This case highlights prostate cancer as a potential cause of cryptogenic stroke and importance of cancer-directed therapy for Trousseau's syndrome.