Myeloproliferative Neoplasm or Reactive Process? A Rare Case of Acute Myeloid Leukemia and Transient Posttreatment Megakaryocytic Hyperplasia with JAK-2 Mutation.

Myeloproliferative neoplasms (MPNs) are hematopoietic malignancies characterized by unchecked proliferation of differentiated myeloid cells. The most common BCR-ABL1-negative MPNs are polycythemia vera, essential thrombocythemia, and primary myelofibrosis. The discovery of JAK2 V617F mutation has improved our understanding of the molecular basis of MPN. The high frequency of JAK2 mutation in MPN makes JAK2 mutation testing an essential diagnostic tool and potential therapeutic target for MPN. Here, we present a rare case of a 34-year-old patient who was initially diagnosed with acute myeloid leukemia (AML) with mutated NPM1. After chemotherapy treatment followed by granulocyte colony stimulating factor administration, the patient achieved complete remission of AML. However, the bone marrow showed hypercellularity with granulocytic hyperplasia, markedly increased atypical megakaryocytes (50.2/HPF) with focal clustering, and reticulin fibrosis (3/4). JAK2 V617F mutation was also detected. Considering the possibility of AML transformed from a previous undiagnosed MPN, patient underwent peripheral blood allogenic stem cell transplant. This case illustrates the diagnostic challenges of firmly establishing a diagnosis between similar, but distinct, disease entities and an accurate clinicopathological differentiation is crucial.