The aim of this multicenter phase 2 trial, Stop Nilotinib (NILSt), was to examine the safety and efficacy of discontinuation of nilotinib in patients with chronic phase (CP)-chronic myelogenous leukemia (CML). Patients with CP-CML who had achieved molecular response (MR4.5) after initiation of imatinib or nilotinib therapy received consolidation therapy with nilotinib 300–400 mg twice daily for up to 24 months. Patients who maintained MR4.5 at 24 months of consolidation therapy proceeded to discontinuation of nilotinib. The study enrolled 149 patients; 112 patients proceeded to consolidation therapy with nilotinib; 90 patients maintained MR4.5 with consolidation therapy, and 87 proceeded to discontinuation of nilotinib. The treatment-free remission (TFR) (MR4.5) rate at both 1 and 3 years after discontinuation of nilotinib was the same, at 60.9% (90% CI 51.6–69.7). Among 34 patients with molecular relapse, nilotinib was resumed in 33 patients; all of them attained MR4.5. There was no significant association between molecular relapse and age, sex, Sokal score, previous interferon-α exposure, duration of tyrosine kinase inhibitors treatment, or trough concentration of nilotinib. With nilotinib, it might be possible to avoid prognostic factors for TFR that exist with imatinib discontinuation. Cessation of nilotinib after two years of consolidation was safe and feasible. Trial registration UMIN000007141.
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