Acute lymphoblastic leukemia (ALL) in infants <1-year-old is biologically different from ALL in older children. Although KMT2A rearrangement is the predominant genetic signature in infantile B-ALL, disease course is heterogenous, behaving more aggressively in younger infants. We investigated clinicopathological differences throughout the first year to understand the transition to pediatric B-ALL. In a multi-institutional review involving four medical institutions, 54 cases of infantile B-ALL were identified. Patients were divided into congenital and non-congenital groups with multiple age subgroups. Male predominance was seen in congenital cases compared to female in non-congenital cases. There were decreasing trends of hyperleukocytosis, central nervous system involvement, KMT2A rearrangements, lineage switch, and mortality, versus increasing trends of CD10 expression and non-KMT2A abnormalities. Statistically significant differences emerged at 3 and 9 months, the latter was not previously described. Poor-prognostic risk factors decreased with age, the last trimester of infantile B-ALL essentially merging with pediatric B-ALL.
Keywords: rearrangements; B-lymphoblastic leukemia; Infantile leukemia; congenital leukemia; lineage switch.