Long-term outcomes after imatinib mesylate discontinuation in chronic myeloid leukemia patients with undetectable minimal residual disease

Background: Imatinib mesylate (IM) discontinuation is under active investigation in chronic myeloid leukemia-chronic phase (CML-CP) patients with undetectable minimal residual disease (UMRD). However, limited data exist on the long-term outcomes following IM discontinuation in patients treated with frontline IM therapy. Methods: We consecutively enrolled patients with CML-CP who discontinued IM after achieving UMRD for ≥12 months between June 2009 and January 2013. Results: Nineteen patients (8 male, 11 female) were included. After IM discontinuation, 14 patients (74%) lost UMRD after a median of 4.0 months. Of the 14 patients with molecular relapses, 12 (86%) relapsed within the first 9 months after IM discontinuation and 2 (14%) relapsed at 20.5 and 22.8 months, respectively. No molecular relapse was observed after 2 years of IM discontinuation. With a median follow-up of 58.1 months (range 23.0-66.5), the estimated UMRD persistence rate at 5 years was 23.7%. IM was readministered in all patients with molecular relapse, and 12 patients (86%) reachieved UMRD at a median of 5.3 months. A high-risk Sokal score, delayed UMRD achievement and short-term IM therapy were significantly associated with molecular relapse. Conclusion: These findings suggest that IM discontinuation in patients who achieved UMRD after frontline IM therapy resulted in favorable long-term outcomes in terms of safety and feasibility.