Session: 617. Acute Myeloid Leukemias: Biomarkers, Molecular Markers and Minimal Residual Disease in Diagnosis and Prognosis: Poster I
Hematology Disease Topics & Pathways:
Research, Acute Myeloid Malignancies, AML, Translational Research, genomics, Diseases, Myeloid Malignancies, Biological Processes
Mutation Profiling: Diagnostic specimens from 1,806 patients with AML (age 0-29 years) enrolled on COG Phase III trials were retrospectively interrogated using contemporary NGS techniques or a PCR based “Tandem Repeat” assay for MYC-ITD. Conventional karyotyping and mutational analysis, including NGS, were used to determine additional cytogenetic and molecular abnormalities. Of the 1,806 patients studied, MYC aberrations were identified in 58 patients (3.2%) with 50% (N=29) harboring MYC-ITD, 46.5% (N=27) with a SNV or indel (MYCSNV/indel) and 2 patients (3.5%) with dual MYC-ITD and SNV. For MYC-ITD, tandem duplications occurred in exon 3 (Max binding domain) with ITD lengths ranging from 252-588 bp. The majority of MYCSNV/indel (77%) were identified at the P72-P78 hotspot with 33.3% (N=9) harboring the P74>L mutation and 18.5% (N=5) having the T73>N mutation.
Functional Studies: Given the novelty of the ITD variant, we initially characterized the functional properties of MYC-ITD in vitro. Similar to wild-type (MYCWT), MYC-ITD is localized to the nucleus and requires Max to bind to specific DNA sequences (E-boxes). However, in contrast to MYCWT, MYC-ITD fails to recognize sequences containing a single E-box in vitro, but exhibits higher affinity toward sequences with two or more E-boxes. MYC-ITD is consistently more efficient in activating promoters with multiple E-boxes than MYCWT. Thus, MYC-ITD may possess different DNA-binding and protein-interacting properties, potentially leading to altered transcriptional regulation and biological output. Given the alterations in DNA binding properties, we evaluated the functional consequences of MYC-ITD in our cord blood stem cell/endothelial cell (EC) co-culture system. Normal cord blood stem cells were transduced with MYC-ITD vs. MYCWT and grown in an EC co-culture system. MYC-ITD transduced cord blood stem cells showed significantly higher proliferation compared to MYCWT or control GFP-transduced cells with proliferation advantage of 37-and 45-fold after 14 and 21 days in co-culture, respectively (p<0.001).
Clinical Impact: Analysis of cooperating cytomolecular lesions revealed a striking difference between MYC-ITD and MYCSNV/indel. MYC-ITD was highly enriched in core-binding factor (CBF) AML found in 86% (N=25)[(N=18, 62%) with inv(16) and (N=7, 24%) with t(8;21)] (Figure 1A), vs. 26% in the MYCWT cohort and had a paucity of somatic mutations. Conversely, MYCSNV/indel was enriched in NUP98-NSD1 fusions (N=7, 27%), FLT3-ITD (N=10, 38%) and NPM1 mutations (N=9, 33%) (Figure 1A), which was significantly higher than the WT cohort. Patients with MYC-ITD had a morphologic CR rate after course 1 of 92.3% vs. 80% (p=0.249) in patients with MYCSNV/indel with a corresponding relapse rate of 24% and 52% (p=0.046). Lower CR and higher relapse reflects the higher proportion of patients with high-risk lesions (FLT3-ITD, NUP98-NSD1 and WT1) in MYCSNV/indel and favorable CBF in MYCITD. Those with MYC-ITD and MYCSNV/indel had a 5-year event free survival (EFS) of 70% vs. 38.5%, respectively (p=0.018) with a corresponding overall survival (OS) of 76% and 47% (p=0.023) similar to patients with favorable or high risk disease (Figure 1B).
Conclusion: Here we define MYC aberrations as a new class of pathogenic variants in childhood AML. We demonstrate functional and clinical characterization of a novel MYC-ITD and contrast this novel variant to that of established pathogenic MYCSNV/indel. We show the high prevalence of co-occurring core-binding factor fusions with MYC-ITD, and high frequency of co-occurring NUP98-NSD1, FLT3-ITD and NPM1 mutations in MYCSNV/indel. Patients with MYC-ITD have superior clinical outcomes while patients with MYCSNV/indel have clinical outcomes similar to high-risk patients, likely due to the associations with the disease associated fusions.
Disclosures: No relevant conflicts of interest to declare.
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