In addition to the genetic screening of these three driver mutations, several authors strongly recommend a search for a BCR-ABL1 fusion gene as an initial step for the diagnosis of MPN insofar as it allows the exclusion of chronic myeloid leukemia, which is the most frequent entity of this group of neoplasms. This evidence concerns the gene ABL1 and chronic myelogenous leukemia, BCR-ABL1 positive.