Background: The feasibility of tyrosine kinase inhibitor (TKI) discontinuation in pediatric chronic myeloid leukemia (CML) remains to be fully elucidated. Procedures: TKI was prospectively discontinued in patients who were diagnosed with CML at <20 years of age, treated with TKI for ≥3 years, and sustained molecular response 4.0 (MR4.0) for ≥2 years. Molecular relapse was defined as a single loss of major molecular response (MMR) (BCR-ABL1IS >0.1%). Relapsed patients resumed the same TKI therapy administered before discontinuation. Results: Twenty-two patients with chronic-phase CML were enrolled, and the median ages at diagnosis and at TKI discontinuation were 9 (range: 1–14) years and 16 (5–26) years, respectively. The median follow-up time after TKI discontinuation was 37 months (range: 24–41 months). The median duration of TKI treatment before discontinuation was 100 (42–178) months, and that of MR4.0 was 53.5 (25–148) months. The treatment-free remission (TFR) rate at 12 months was 50.0% (90% confidence interval: 31.7%–65.8%). Eleven patients experienced loss of MMR within 4 months after TKI discontinuation and resumed TKI as originally prescribed. No progression was observed, and all 11 patients regained MR4.0 after TKI resumption. No patient had a withdrawal syndrome. The quality-of-life analysis suggested that successful TFR may improve academic performance in some patients. In patients who discontinued TKI therapy before puberty, the possibility of improvement in growth velocity upon TKI discontinuation was observed. Conclusions: TKI could be discontinued safely in patients with pediatric CML showing a sustained deep MR.
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