Molecular responses of late chronic phase chronic myeloid leukemia patients after achieving complete cytogenetic responses with imatinib treatment: a 6-year follow-up

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To explore the long-term efficacy of imatinib to chronic myeloid leukemia, a total of 46 late chronic phase (CP) patients were assessed after achieving complete cytogenetic response (CCyR). The median duration of imatinib treatment was 68 (61–74) months. Two hundred fifty-three bone marrow samples were detected BCR–ABL messenger RNA (mRNA) levels by TaqMan-based real-time quantitative reverse transcription–polymerase chain reaction. The median time when CCyR was first achieved was eight (3–72) months. Thirty-four patients achieved major molecular response (MMoR), and their median time when MMoR was first achieved was 35 (3–65) months. More patients achieving CCyR within 18 months obtained MMoR than those after 18 months (85% vs 42%, p = 0.006). One patient progressed into blastic crisis, and four patients suffered cytogenetic relapse later. The estimated 6-year event-free survival (EFS) rate of all patients was 81%. The BCR–ABL mRNA levels at the time of first CCyR of relapsed patients were significantly higher than those in continuous CCyR (p = 0.011). The 6-year estimated EFS rate of MMoR patients was significantly higher than that of non-MMoR patients (100% vs 44%, p = 0.0001). Achieving CCyR within 18 months had a higher probability of achieving MMoR within 6 years. The 6-year estimated EFS rate was significantly higher for patients achieving CCyR within 12 months than those after 12 months (97% vs 55%, p = 0.05). The time when MMoR was first achieved did not affect 6-year estimated EFS. Therefore, imatinib could induce most late CP patients to achieve long-term durable responses after achieving CCyR. Both the time when CCyR was first achieved and the depth of BCR–ABL reduction after CCyR are relevant to long-term EFS.

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