However, it is important to note that a worse MPN course, i.e., increased risk of transformation of ET to secondary myelofibrosis, splenomegaly, aspirin-induced hemorrhage, and worsened survival, was also observed in patients harboring a CALR 52 bp deletion and 5 bp insertion [10,17,18,27,28,29,30,31,32]. This evidence concerns the gene CALR and myeloproliferative disorder.