Abstract
B/T mixed phenotype acute leukemia (MPAL) is a rare aggressive leukemia. Three cases of B/T MPAL were identified with comprehensive immunophenotypic, cytogenetic, and molecular studies. T-lineage predominant B/T MPAL shares a genetic signature with T-ALL whereas B/T lineage co-dominant B/T MPAL lacks such a T-ALL signature. All three patients were treated with lineage-matched-ALL therapy and alive at the last follow-up. Our study is the first to demonstrate molecular heterogeneity within B/T MPAL in a context of an immunophenotype of T-lineage versus B-lineage predominance. The implication of such a phenotype-genotype association on diagnostic classification is briefly discussed.