JAK2 and chronic myelomonocytic leukemia: There are several criteria used in the clinic to diagnose CMML, such as persistent absolute monocytosis (≥1 × 109/L), with monocytes accounting for more than 10% but less than 20% of leucocytes (WBC—white blood cells) in the peripheral blood, dysplasia in one or more bone marrow (BM) cell lineage, and the absence of genetic rearrangements in the PDGFRA, FDGFRB, and FGFR1 genes and the PCM1-JAK2 and BCR-ABL1 fusions [13,14,15] (Figure 1).