Essential thrombocythemia (ET) is a chronic myeloproliferative disorder (MPD) that involves primary the megakaryocytic lineage. It is characterized by sustained thrombocytosis in the blood, increased numbers of large, mature megakaryocytes in the bone marrow, no recurrent genetic defects, and clinically, by episodes of thrombosis and/or hemorrhage.  The disease can evolve into myelofibrosis and rarely into acute leukemia [1, 2].

According to the criteria of the Polycythemia Vera Study Group (PVSG), the diagnosis of ET requires lack of features diagnostic for other MPDs, including the Philadelphia (Ph) chromosome [3]. The Ph chromosome is specific for chronic myelogeneus leukemia (CML) and it's detection is applied to differentiate CML from other MPDs. The molecular counterpart of the Ph chromosome is the BCR-ABL gene. This gene codes a fusion protein with transforming ability and plays a central role in the pathogenesis of CML [4, 5].

Recently, some authors reported that BCR-ABL transcripts are detectable in approximately half of Ph chromosome negative ET patients, with a possible impact on the prognosis of the disease (6-9). However, other investigators did not confirm these observations (10-13). To further address this issue we investigated the presence of the BCR-ABL gene in a cohort of ET patients with a long follow-up.