Second Imatinib Discontinuation Outcomes in Patients Regaining Durable Deep Molecular Response in the Korean Imatinib Discontinuation Study; KID Study

Backgroud: Although multiple trials have shown that stopping tyrosine kinase inhibitor (TKI) treatment can be employed in CP CML patients with sustained deep molecular response (DMR) after enough TKI therapy, they emphasized the need for close monitoring because about 50-70% of patients experienced molecular relapse. However, most patients with molecular recurrence regain their initial molecular level after restarting TKI therapy.

Aims: In this study, we analyzed second imatinib (IM) discontinuation outcomes in patients regaining durable DMR in the Korean multicenter prospective study (Korean Imatinib Discontinuation Study; KID Study)

Methods: CP CML patients who were treated with IM for more than 3 years and maintained DMR for at least 2 years were eligible for the Korean multicenter prospective study and in cases of MMR loss on 2 consecutive assessments, IM treatment was re-introduced. After IM resumption, the molecular response was evaluated every month until re-achievement of MMR and every 3 months thereafter. The second stop was permitted in the patients who were in second DMR for at least 2 years.

Results: Among the patients who maintained a second DMR for at least 2 years after IM resumption, 23 patients entered into a second IM stop. Prior to first discontinuation, the median duration of IM therapy was 73.2 months (range, 38.4-133.2 months) and the duration of sustained UMRD was 38.4 months (range, 24-102 months). After first attempt of IM discontinuation, they relapsed after a median duration of 3.7 months (range, 1.8-20.8 months) and re-achieved UMRD at a median of 5.8 months (range, 1.7-12.1 months) after IM resumption. After sustaining a second DMR for a median of 26.3 months, IM therapy discontinued for a second time.

With a median follow-up of 29.5 months (range, 9-63 months) since second IM stop, 15/23 patients (65%) lost MMR after a median 2.9 months (range, 1.8-30.7 months), which was similar to those of the first IM discontinuation [median 3.7 (range, 1.8-20.8 months)]. The patients who lost MMR were retreated with IM for a median of 24.5 months (range, 1.2-49.7 months); 14 patients re-achieved MMR and one patient was in therapy for 1.2 months.

Conclusion: Our data demonstrated that a second attempt might be possible and the median time to MMR loss after second discontinuation was similar to those of the first discontinuation. Further studies on the predictors to select patients for a trial of second TFR and novel strategies will be warranted.