ABL1 and chronic myelogenous leukemia, BCR-ABL1 positive: 147 patients with CML (aged ≥ 18 years) in chronic phase, who are treated with imatinib, bosutinib, dasatinib, nilotinib or ponatinib, and have reached at least major molecular response (defined as having BCR-ABL levels < 0.1% for an uninterrupted period of 6 months) are eligible.