Previous studies have suggested that CML stem cells might be more primitive stem cells than multipotent HSCs when the BCR/ABL fusion gene in haemangioblastic-like cells have been identified [4] while other studies found the BCR/ABL fusion gene in even more primitive progenitor cells defined as Flk1+, CD31-, CD34- [5]. This evidence concerns the gene ABL1 and chronic myelogenous leukemia, BCR-ABL1 positive.