Asciminib for Pediatric Chronic Myelogenous Leukemia

Key Inclusion Criteria: Participants eligible for inclusion in this study must meet all of the following criteria: 1. Signed informed consent must be obtained prior to participation in the study. 2. Male or female participants 1 and \< 18 years of age at study enrollment 3. Diagnosis of CML-CP (Apperley et al 2025) with cytogenetic confirmation of Philadelphia positive (Ph+) chromosome 4. For participants with CML-CP newly diagnosed within 3 months of screening OR 5 For participants with CML - CP with high risk of developing resistance or intolerance to previous TKI: 1. Unfavourable response to TKI is defined following the Apperley et al 2025 guidelines as: * At three months after the initiation of therapy: BCR::ABL1 ratio \> 10% IS (if confirmed within 1-3 months) * At six months after the initiation of therapy: BCR::ABL1 ratio \> 10% IS * At twelve months after initiation of therapy: BCR::ABL1 ratio \> 1% IS * At any time loss of previous response * At any time emergent resistant BCR::ABL1 mutations or high-risk ACA from prior TKI treatment as per local test results 2. Intolerance to TKI is defined as: * Non-hematologic intolerance: participants with grade 3 or 4 toxicity while on therapy (in which case the patient is eligible whether or not there was a dose reduction); or with persistent grade 2 toxicity unresponsive to optimal management including dose adjustments (unless dose reduction is not considered in the best interest of the patient if response is already suboptimal) * Hematologic intolerance: participants with grade 3 or 4 toxicity (absolute neutrophil count \[ANC\] or platelets) while on therapy that is recurrent after dose reduction to the lowest doses of the TKI 6\. Evidence of typical BCR::ABL1 transcript \[e14a2 and/or e13a2\] at the time of screening which are amenable to standardized RQ-PCR quantification. 7\. Performance status: Karnofsky ≥ 50% for participants ≥ 16 years of age, and Lansky ≥ 50 for participants \< 16 years of age at the time of screening. Key Exclusion Criteria: 1. Known second chronic phase (CP) of CML after previous progression to Accelerated Phase (AP)/Blast Phase (BP). 2. Previous treatment with a hematopoietic stem-cell transplantation. 3. Patient planned to undergo allogeneic hematopoietic stem cell transplantation 4. Known presence of a BCR::ABL1 mutation with known resistance to study treatment in accordance with the most recent public version of international CML clinical guidelines (e.g. NCCN CML treatment guidelines v 1.2026 and Apperley et al 2025) any time prior to study entry Other inclusion/exclusion criteria may apply.