- The case of an 11-year-old child with adult-type chronic myeloid leukemia, Philadelphia ( BCR-ABL ) positive, reverse transcription–polymerase chain reaction negative for the major, minor, and micro breakpoints is presented. In the course of 3 years, the child failed to respond to treatment with hydroxyurea, refused all therapy for 6 months, was intolerant to α-interferon and progressed, while on imatinib, to acute basophilic leukemia. Subsequently he underwent successful bone marrow transplantation. A secondary cytogenetic clonal evolution, i(17q), developed during hydroxyurea treatment and a tertiary clonal evolution, +8, was detected during imatinib treatment. It is not clear to what extent the several factors (undefined BCR-ABL breakpoint, treatment avoidance, and initial treatment choices, alone or in combination) played a role in the imatinib relapse and resistance and in the disease progression. We conclude that close follow-up with frequent bone marrow sampling is crucial in order to monitor such patients for early relapse and prompt referral for bone marrow transplant.