Clinical value of assessing the response to imatinib monitored by interphase FISH and RQ-PCR for BCR-ABL in peripheral blood for long-term survival of chronic phase CML patients: results of the Niigata CML-multi-institutional co-operative clinical study

This retrospective analysis investigated the prognostic value of monitoring the response to imatinib using peripheral blood (PB) samples and the impact of the response on outcome in 133 patients with chronic myeloid leukemia (CML). We divided the response into 3 categories according to the results of neutrophil (N)-FISH and BCR-ABL transcript levels in PB; more than a 3-log reduction [major molecular response (MMR)], between a 2-log and 3-log reduction or negative with N-FISH [complete cytogenetic response equivalent (CCyRe)], N-FISH positive or less than a 2-log reduction (non-CCyRe). The median follow-up was 5.46 years. At 5 years, the overall survival (OS) rate and progression-free survival (PFS) rate were 94.4 and 92.0%, respectively. The estimated rate of the CCyRe and MMR were 81.7 and 67.1%, respectively. 106 patients achieving the CCyRe had significantly better OS and PFS than 27 patients without achieving the CCyRe. Patients with MMR had significantly better survival free from death, progression, imatinib withdrawal and a loss of the CCyRe, than patients whose response level remained in the CCyRe without achieving MMR until 18 months. Our observation suggests that the response level of the CCyRe on PB serve as a prognostic indicator, and achieving MMR provides stable long-term survival.