JAK2 and myelodysplastic syndrome: From a molecular point of view, the most relevant element is the frequent co-occurrence of somatic SF3B1 mutations, found in approximately 80% of the MDS/MPN-T cases, together with the JAK2 V617F mutation, found in 50–60%, or less commonly, with CALR or MPL mutations, globally found in less than 10% of the MDS/MPN-T cases.