BCR and chronic myelogenous leukemia, BCR-ABL1 positive: The time to PoC studies with imatinib, once it had been identified in screens as a selective BCR:ABL inhibitor and Mode of Action had been demonstrated by selective killing of CML cells in vitro and in vivo models, was also short and comparable to the timeframe of Mode of Action and PoC transitions in the case of ATRA and ATO in APL.