Pediatric Essential Thrombocythemia With a Novel CALR Mutation: A Case Report

Pediatric essential thrombocythemia (ET) is extremely rare and frequently lacks identifiable driver mutations. We report a case of a 5‐year‐old male with ET harboring a novel CALR exon 9 frameshift mutation complicated by acquired von Willebrand syndrome. The patient presented with purpura, extreme thrombocytosis (1900 × 10 9 /L), and reduced von Willebrand factor activity. Antiplatelet therapy was avoided because of bleeding risk, and anagrelide was initiated. Treatment was associated with reduction in platelet count and improvement in von Willebrand factor activity. This case expands the molecular spectrum of pediatric CALR ‐mutated ET and highlights the importance of individualized management in children with extreme thrombocytosis. Trial Registration The authors have confirmed clinical trial registration is not needed for this submission.