Hydroxyurea (HU) induces molecular response and suppresses the T315I-positive sub-clone(s) in advanced CML. Four heavily pretreated CML patients (#1–#4) were treated with HU, BCR-ABL1 tyrosine kinase inhibitors (imatinib, 400 mg/day; dasatinib, 100 mg/day; nilotinib, 2 × 400 mg/day per os), polychemotherapy, or hematopoietic stem cell transplantation (HSCT) as indicated. The percentage of BCR-ABL1 mRNA relative to ABL1 mRNA (according to the international scale) as well as the percentage of BCR-ABL1T315I mRNA relative to BCR-ABL1 mRNA (BCR-ABL1T315I/BCR-ABL1, determined by ligase-dependent PCR) are shown in the upper panels. The white blood count (WBC) of the same patients are shown in the lower panels. 3 + 7: combined chemotherapy following the 3 + 7-protocol consisting of daunorubicine (60 mg/m2 per day, days 1–3) and cytosine arabinoside (200 mg/m2 per day, days 1–7).