Myeloproliferative neoplasms (MPN) are clonal diseases of hematopoietic stem cells characterized by the hyperplasia of one or more myeloid cell lines that retain their capacity for terminal differentiation [1]. Three entities that share overlapping but distinct clinical and laboratory characteristics are referred to as Philadelphia chromosome-negative (or BCR-ABL-negative) MPN: polycythemia vera (PV), essential thrombocythemia (ET), and primary myelofibrosis (PMF). The incidence of ET in Europe is estimated to be 0.4 to 1.7 per 100,000 person-years [2].
