Int J Mol Sci

B-cell acute lymphoblastic leukemia (B-ALL) remains a major clinical challenge in hematologic oncology, characterized by a continuous evolution of molecular drivers that shape its heterogeneity across the age spectrum. Pediatric B-ALL is generally associated with high cure rates, while adult forms of the disease are often more aggressive and less responsive to treatment. This review examines the age-specific genetic and epigenetic landscapes that contribute to this disparity, revealing how the nature and timing of molecular alterations point to fundamentally different leukemogenic processes. Favorable genetic aberrations, such as ETV6::RUNX1 and hyperdiploidy, are predominant in children, whereas adults more frequently present with high-risk features, including BCR::ABL1 fusions and IKZF1 deletions. Epigenetic distinctions are similarly age-dependent, involving divergent patterns of DNA methylation, histone modifications, and non-coding RNA expression. For example, pediatric B-ALL frequently harbors mutations in epigenetic regulators like SETD2 and CREBBP, while adult B-ALL is more commonly affected by alterations in TET2 and IDH1/2. These molecular differences are not only prognostic but also mechanistic, reflecting distinct developmental trajectories and vulnerabilities. Understanding these age-driven transitions is essential for improving risk stratification and developing precision therapies tailored to the unique biology of B-ALL across the lifespan.