BCR and chronic myelogenous leukemia, BCR-ABL1 positive: Drug resistance is associated with the reactivation of BCR–ABL signal transduction of those patients who start Imatinib in the early chronic, late chronic and accelerated phase of CML; 12%, 32%, and respectively 62% of CML patients in early chronic, late chronic and accelerated phase develop resistance mutations within 2 years from the first administration of the treatment.