Since BCR-ABL by itself appeared to be insufficient to induce leukemia in xenograft models, it has been proposed that additional pathways might be necessary to cooperate with BCR-ABL in the transition from CP-CML into BC-CML, such as the Wnt and Hedgehog pathways [16, 56, 57]. This evidence concerns the gene ABL1 and chronic myelogenous leukemia, BCR-ABL1 positive.