JAK2 and essential thrombocythemia: Tabaczewski et al. [6] reported cases of CLL coexistent with JAK2 V617F positive essential thrombocythemia and set the hypothesis that during the pre-JAK2 phase of the stem cell development, an initial genetic hit occurred that predisposed the pluripotent stem cell to further genetic mutations and then stem cells differentiated into myeloid and lymphoid lineages.