Case Report: Chronic myeloid leukemia masquerading as essential thrombocythemia in a child: the imperative for early BCR::ABL1 testing in isolated thrombocytosis.

Chronic myeloid leukemia (CML) is a rare hematologic malignancy in children, typically presenting with leukocytosis in the peripheral blood, and often accompanied by symptoms such as fever or splenomegaly. This report describes a rare pediatric case of CML that manifested solely as isolated thrombocytosis. Due to this atypical presentation, the patient was initially misdiagnosed with essential thrombocythemia (ET) and treated with hydroxyurea and aspirin, which yielded no clinical response. The diagnosis of CML was subsequently confirmed by detection of the BCR::ABL1 fusion gene. Upon confirmation, the patient was promptly initiated on imatinib therapy and achieved a complete cytogenetic response within 4 months. We also conducted a literature review of similar cases, discussing their prognosis and differential diagnosis with ET, and recommend early BCR::ABL1 fusion gene testing in all pediatric patients presenting with isolated thrombocytosis to ensure accurate diagnosis.