Polycythemia vera (PV), essential thrombocythemia (ET), and primary myelofibrosis (PMF), due to their clinical, morphological, and molecular features, are organized into Philadelphia-negative classical MPNs or BCR-ABL-negative classical MPNs [4,5,6]; they are distinguished by extramedullary hematopoiesis and a predisposition for fibrosis, hemorrhage, arterial and venous thrombosis, and the possibility to change into acute leukemia [7]. Here, ABL1 is linked to acquired polycythemia vera.