Clinical and molecular genetic characterization of wild-type MLL infant acute lymphoblastic leukemia identifies few recurrent abnormalities

Wild-type MLL infant acute lymphoblastic leukemia (ALL) patients account for approximately 20% of all infant ALL cases. Although this group of patients generally fares better than MLL-rearranged infant ALL patients, their prognosis is still worse than that of non-infant pediatric B-ALL patients. Extensive characterization of this specific patient group largely remains unacknowledged. In this study, we aim to obtain a clinical and molecular profile of this patient group in order to find new opportunities to optimize treatment. We report on a large cohort of 78 wild-type MLL infant ALL samples using clinical parameters, array-comparative genomic hybridization analysis, and gene expression profiling. The frequency of DNA copy number variations and molecular genetic lesions in genes involved in B-cell development are lower in wild-type MLL infant ALL than older children with ALL. Wild-type MLL infant ALL presented with higher white blood cell (WBC) counts and a more immature immunophenotype than pediatric (non-infant) B-ALL patients. The strongest predictor of outcome in wild-type MLL infant ALL was the level of MEIS1 expression, which may indicate new opportunities for novel strategies in treating wild-type MLL infant ALL.