Usually, Chronic Myeloid Leukemia (CML), a well characterized entity harbouring the recurrent t(9;22) translocation and the resulting BCR-ABL1 fusion gene, is separated from the classical MPDs such as Polycythemia Vera (PV), Essential Thrombocytemia (ET) and Primary Myelofibrosis (PMF), in which a molecular abnormality has long time been ignored. The gene discussed is ABL1; the disease is essential thrombocythemia.