Acute Myeloid Leukemia With RUNX1::RUNX1T1 Fusion Transformed From JAK2V617F-Mutated Polycythemia Vera: A Case Report

Leukemic transformation is an event that significantly affects the prognosis of patients with Philadelphia chromosome-negative myeloproliferative neoplasms (MPNs). In acute myeloid leukemia (AML) transformed from MPNs, balanced chromosomal translocations, including t(8;21)(q22;q22.1), are extremely rare. A case of secondary AML with <i>RUNX1</i>::<i>RUNX1T1</i> fusion that evolved from polycythemia vera (PV) is presented. An 87-year-old Japanese man was diagnosed with PV 22 years earlier and had been treated with hydroxyurea and aspirin. Twelve years earlier, a homozygous <i>JAK2</i>V617F mutation was identified. Regular blood tests conducted every four months showed leukocytosis (white blood cell count, 14.6 × 10⁹/L), anemia (hemoglobin, 106 g/L), and thrombocytopenia (platelet count, 73 × 10⁹/L). Of the white blood cells, 5.5% were blasts, and the pseudo-Pelger-Huët anomaly and degranulated neutrophils were also observed. Bone marrow aspiration showed 18.2% myeloblasts with varying morphology, characterized by basophilic cytoplasm and wide cytoplasm containing numerous azurophilic granules and perinuclear hofs. The appearance of neutrophils with pink-colored cytoplasm was also noted. Flow cytometry (FCM) showed positivity for myeloid markers, as well as CD34 and CD19, and myeloperoxidase was strongly positive. Morphological findings and FCM results were highly suggestive of AML with the <i>RUNX1</i>::<i>RUNX1T1</i> fusion gene. Chromosomal analysis identified a translocation t(8;21)(q22;q22.1), and the real-time quantitative polymerase chain reaction detected the <i>RUNX1</i>::<i>RUNX1T1</i> fusion gene. Based on these findings, the patient was diagnosed with AML with <i>RUNX1</i>::<i>RUNX1T1</i> fusion that had transformed from PV. In addition, <i>the JAK2</i>V617F mutation (homozygous) was detected in peripheral blood at the time of transformation to AML. Leukemic evolution from MPNs often involves morphological changes in addition to genetic and chromosomal abnormalities. Therefore, during the follow-up of MPN, it is important to focus on changes in the blood cell morphology.