Recurrent genetic fusions redefine MLL germ line acute lymphoblastic leukemia in infants

B-cell precursor (BCP) acute lymphoblastic leukemia (BCP-ALL) in infants (ie, children age <1 year) is a rare disease traditionally subdivided into MLL-rearranged (alias KMT2A; MLL-R) and MLL germ line (MLL-G) subtypes. MLL gene rearrangements occur in ∼75% of infants with BCP-ALL1-3 and are typically associated with a mixed-lineage phenotype.4 MLL rearrangements originate prenatally in utero5 and play a role in transcription factor dysregulation.6 MLL-R BCP-ALL in infants is associated with dismal outcomes.1-3 Infants with MLL-G ALL treated with intensive therapies in the Interfant-06 protocol may have a relatively favorable prognosis, with a 6-year event-free survival (EFS) rate of 73.9%,2 slightly inferior to that observed in older children with BCP-ALL.1,2 Of interest, a recent study from the Japanese Pediatric Leukemia/Lymphoma Study Group MLL-10 trial reported more favorable outcomes in infants