BCR and myeloproliferative disorder: However, several studies presented an opposing view, showing presence of 2 different clones or subclones, which can grow independently from each other.[6,14–18] For example, a recent MPN study[11] of concurrent BCR-ABL1 fusion and JAK2 mutation indicated that some JAK2+ MPN cells acquired BCR-ABL1 fusions, whereas others had both genetic drivers at the initial diagnosis, suggesting that 2 independent clones arose from genetically unstable hematopoietic stem and progenitor cells and then competed with each other.