Treatment‐Free Remissions in Children With Chronic Myeloid Leukemia (<scp>CML</scp>): A Prospective Study From the Tata Memorial Hospital (<scp>TMH</scp>) Pediatric <scp>CML</scp> (<scp>pCML</scp>) Cohort

Pediatric chronic myeloid leukemia (pCML) is a rare childhood malignancy, representing 2%-3% of all childhood leukemia. Tyrosine kinase inhibitors (TKIs) have greatly improved survival but pose challenges due to their long-term effects on growth and bone health in children. We prospectively studied treatment-free remission (TFR) in 45 children with pCML in chronic phase on imatinib. Eligibility criteria were as per current NCCN guidelines, with a less stringent qPCR monitoring scheduled every 3 months. TFR was successful in 71.1% (32 out of 45) of patients after a median follow-up of 25 (range: 6-42) months. The TFR rates at 12 and 24 months were 70% and 66%, respectively. Children under 5 years had a TFR rate of 88.9%, compared to 61.8% in those over 5 years (p = 0.18). Eleven of the 13 patients who lost MMR did so within 6 months of discontinuation. The cumulative incidence of loss in MMR at 6, 12, and 24 months was 26.4%, 27%, and 33%, respectively. Ten out of 13 (76.9%) patients with discontinuation failure (DF) regained MMR within 3 (2-20) months of restarting imatinib. A significant correlation was found between higher T-regulatory cell levels at baseline and DF (p = 0.005). More than half patients showed improved bone mineral density after 2 years of TFR. Our findings suggest that high TFR rates can be attained in pCML, with added benefits for bone health. Less frequent molecular monitoring was not associated with adverse outcomes and there seems to be a role of the immune system in sustaining TFR. The study is registered in the Clinical Trials Registry-India (CTRI/2020/11/029199).