IFNA1 and myelofibrosis: Treatment with IFN is associated with drop‐out rates of 20%‐30% and in some studies even up to 40% due to toxic side effects.37, 38, 39, 40, 41, 42, 43 It has been speculated whether intolerance to IFN is also dependent upon disease stage, implying more toxic side effects in the advanced myelofibrosis stage and less so in the early disease stages.