Treatment-free remission of chronic myeloid leukemia in real-world practice by the detection limit of MR4.3.

BACKGROUND: Molecular response (MR) 4.0 or 4.3 remains an indicator of treatment-free remission (TFR) in patients with chronic myeloid leukemia (CML) in countries that accept it as the criterion of undetectable minimal residual disease (UMRD) in clinical practice. We retrospectively analyzed the TFR outcomes to identify the clinical efficacy of MR4.0/4.3 as the UMRD criterion. PATIENTS AND METHODS: CML patients treated with tyrosine kinase inhibitors (TKIs) between March 2001 and May 2015 for >3 years and treatment cessation for over 6 months were included. TFR was analyzed using MR3.0 loss and UMRD loss as criteria. TFR failure-free survival was defined as the time from cessation of TKI therapy to MR loss or restarting TKI, and overall survival as the time from TKI cessation to death. The probability of regaining the MR was evaluated. RESULTS: In the 93 participants, the median duration of follow-up and TKI therapy were 17.3 (3.9-92.0) months and 7.4 (3.1-16.9) years, respectively. TFR at 5 years was 47.9 % and 44.4 %, for MR3.0 loss and UMRD loss, respectively. Among the 42 patients who restarted TKI, 41 regained MR3.0 (97.6 %). In multivariate analysis, the time to UMRD was ≤12 months, and the absence of prior TKI treatment (P = 0.018 and 0.044 in UMRD loss, respectively) was significantly correlated with TFR failure-free survival. CONCLUSION: Clinical outcomes were comparable to those of clinical trials. Our results suggest that the detection limit of MR4.3 can be used in clinical practice for TKI treatment cessation for TFR in CML patients.