An extensive analysis of mixed phenotype acute leukemia (MPAL) has led to new insights that may have implications for disease classification and treatment.
Researchers believe they have identified new subtypes of MPAL that should be included in the World Health Organization classification for acute leukemia.
Each of these subtypes share genomic characteristics with other acute leukemias, which suggests they might respond to treatments that are already in use.
This research also has shed light on how MPAL evolves and appears to provide an explanation for why MPAL displays characteristics of both acute myeloid leukemia (AML) and acute lymphoblastic leukemia (ALL).
“ALL and AML have very different treatments, but MPAL has features of both, so the question of how best to treat patients with MPAL has been challenging the leukemia community worldwide, and long-term survival of patients has been poor,” said study author Charles G. Mullighan, MD, of St. Jude Children’s Research Hospital in Memphis, Tenn.
In the current study, published in Nature, Dr. Mullighan and his colleagues used whole-genome, whole-exome, and RNA sequencing to analyze 115 samples from pediatric patients with MPAL.
The analysis revealed mutations that define the two most common subtypes of MPAL – B/myeloid and T/myeloid – and suggested these subtypes share similarities with other leukemia subtypes.
The researchers found that 48% of B/myeloid MPAL cases carried rearrangements in ZNF384, a characteristic that is also found in cases of B-cell ALL. In fact, the team said the gene expression profiles of ZNF384r B-ALL and ZNF384r MPAL were indistinguishable.
“That is biologically and clinically important,” Dr. Mullighan said. “The findings suggest the ZNF384 rearrangement defines a distinct leukemia subtype, and the alteration should be used to guide treatment.”
The researchers noted that patients with ZNF384r exhibited higher FLT3 expression than that of patients with other types of B/myeloid or T/myeloid MPAL, so patients with ZNF384r MPAL might respond well to treatment with a FLT3 inhibitor.
This study also showed that cases of B/myeloid MPAL without ZNF384r shared genomic features with other B-ALL subtypes, such as Ph-like B-ALL.
In addition, the analysis showed that T/myeloid MPAL and early T-cell precursor ALL have similar gene expression profiles.
The team identified several genes that were mutated at similar frequencies in T/myeloid MPAL and early T-cell precursor ALL, including WT1, ETV6, EZH2, and FLT3.
WT1 was the most frequently mutated transcription factor gene in T/myeloid MPAL.
Based on these findings, the researchers said the WHO classification of acute leukemia should be updated to include: ZNF384r acute leukemia (either B-ALL or MPAL), WT1-mutant T/myeloid MPAL, and Ph-like B/myeloid MPAL.
This research was supported by the National Cancer Institute, the National Institutes of Health, Cookies for Kids’ Cancer, and other organizations. The researchers reported having no competing interests.
SOURCE: Alexander TB et al. Nature. 2018 Sep 12. doi: 10.1038/s41586-018-0436-0.