T he aim of the Korean Imatinib Discontinuation Study was to identify predictors for safe and successful imatinib discontinuation. A total of 90 patients with a follow-up of ≥12 months were analyzed. After a median follow-up of 26.6 months after imatinib discontinuation, 37 patients lost the major molecular response. The probability of sustained major molecular response at 12 months and 24 months was 62.2% and 58.5%, respectively. All 37 patients who lost major molecular response were retreated with imatinib therapy for a median of 16.9 months, and all achieved major molecular response again at a median of 3.9 months after resuming imatinib therapy. We observed newly developed or worsened musculoskeletal pain and pruritus in 27 (30%) patients after imatinib discontinuation. Imatinib withdrawal syndrome was associated with a higher probability of sustained major molecular response (P=0.003) and showed a trend for a longer time to major molecular response loss (P=0.098). Positivity (defined as ≥ 17 positive chambers) of digital polymerase chain reaction at screening and longer imatinib duration before imatinib discontinuation were associated with a higher probability of sustained major molecular response. Our data demonstrated that the occurrence of imatinib withdrawal syndrome after imatinib discontinuation and longer duration of imatinib were associated with a lower rate of molecular relapse. In addition, minimal residual leukemia measured by digital polymerase chain reaction had a trend for a higher molecular relapse.

Key Points Mutation clearance in CML does not directly result in successful treatment in CML. Clinical implications of patterns of mutation acquisition, persistence, and clearance in CML should be interpreted with caution.

PURPOSE Patients with chronic myelogenous leukemia in accelerated phase (CML-AP) that is resistant or intolerant to imatinib have limited therapeutic options. Dasatinib, a potent inhibitor of BCR-ABL and SRC-family kinases, has efficacy in patients with CML-AP who have experienced treatment failure with imatinib. We now report follow-up data from the full patient cohort of 174 patients enrolled onto a phase II trial to provide a more complete assessment of the efficacy and safety of dasatinib in this population. PATIENTS AND METHODS Patients with imatinib-resistant (n = 161) or -intolerant (n = 13) CML-AP received dasatinib 70 mg orally twice daily. Results At a median follow-up of 14.1 months (treatment duration, 0.1 to 21.7 months), major and complete hematologic responses were attained by 64% and 45% of patients, respectively, and major and complete cytogenetic responses were achieved in 39% and 32% of patients, respectively. Responses were achieved irrespective of imatinib status (resistant or intolerant), prior stem-cell transplantation, or the presence of prior BCR-ABL mutation. The 12-month progression-free survival and overall survival rates were 66% and 82%, respectively. Dasatinib was generally well tolerated; the most frequent nonhematologic severe treatment-related adverse event was diarrhea (52%; grade 3 to 4, 8%). Cytopenias were common, including grade 3 to 4 neutropenia (76%) and thrombocytopenia (82%). Pleural effusion occurred in 27% of patients (grade 3 to 4, 5%). CONCLUSION Dasatinib is effective in patients with CML-AP after imatinib treatment failure.