Hyperdiploidy impairs fetal hematopoietic progenitor fitness and differentiation enabling persistence of rare preleukemic aneuploid clones. - Thampi N; Calvo C; Rodríguez-Cortez V; Martínez-Moreno A; Roca-Ho H; Vinyoles M; Bueno C; Espinosa-Aroca L; Pablo-Fontecha V; Camps J; de la Fuente-González A; Puente XS; et al. (Cell reports, 2026)