These observations are comparable to the findings that both ruxolitinib and fedratinib have been demonstrated to have clinical responses in MPN patients harboring CALR mutations.45, 46, 47 However, fedratinib has less hematological toxicities than ruxolitinib especially thrombocytopenia, which is a dose-limiting toxicity of ruxolitinib.42, 43, 44 Despite both JAK inhibitors are effective in the reduction of splenomegaly and the relief of clinical symptoms, they are not likely to substantially modify the natural history of the BCR-ABL-negative classic MPNs including CALR-mutated PMF. The gene discussed is ABL1; the disease is Splenomegaly.