Defining 2 biologically and clinically distinct groups in acute leukemia with a mixed phenotype.

A mixed phenotype (MP) is a characteristic of de novo MP acute leukemia (MPAL), but it can also be found in other leukemias. It poses substantial classification and management dilemmas. Herein, we report a large cohort of acute leukemia with MP and define acute myeloid leukemia with MP (AML-MP) and MPAL as 2 distinct groups by characterizing clinical, genetic, and transcriptomic features. Clinically, patients with AML-MP and MPAL were both treated with either AML- or acute lymphoblastic leukemia (ALL)-directed induction regimens. AML-MP has inferior responses (hazard ratio, 12.5; 95% confidence interval, 2.72-57.8; P = .001), whereas MPAL has better responses to ALL-directed treatment. Genetically, AML-MP harbors more frequent RUNX1 (23/52 [44%]) and TP53 (12/52 [23.1%]) mutations. In contrast, RUNX1 mutations are less frequent in MPAL (8/35 [23%]; P = .01 vs AML-MP) and TP53 mutations as a driver are virtually absent in MPAL. Transcriptionally, AML-MP shows enrichment for stemness signatures and a relative deficit of transcription factors critical for myeloid and lymphoid differentiation. Furthermore, AML-MP rarely switches to a lymphoid immunophenotype after treatment, in contrast to MPAL (1/40 [2.5%] vs 10/28 [35.7%]; P = .0003). Last, a genomic classification framework is proposed for future studies. Together, these data support the designation of AML-MP as a diagnosis distinct from MPAL and provide novel insights into the pathogenesis and therapies of acute leukemia with MP.