Abstract
INTRODUCTION: In general, platelet counts fluctuate in cancer patients receiving anticancer therapy. It may include thrombocytopenia caused by bone marrow suppression due to cytotoxic anticancer agents and thrombocytosis due to rebound during recovery. This should not be the case in the case of administration of immune checkpoint inhibitors, given their mechanism of action. CASE PRESENTATION: However, we have experienced a case of thrombocytosis in a patient treated with an immune checkpoint inhibitor. We present a platelet count pattern in patient with bladder cancer underwent Gemcitabine and Cisplatin (GC) therapy and pembrolizumab monotherapy. CONCLUSION: This case underscores the need for a diverse perspective on platelet behavior in clinical settings.