Abstract 3954: Increased mosaic chromosomal alterations among survivors of childhood acute myeloid leukemia

Abstract Background: We previously characterized point mutations of clonal hematopoiesis (CH) including single nucleotide variants or small insertion/deletions residing in a set of cancer-related genes (e. g. , DNMT3A and TET2), and found that CH point mutations occurred at a much higher prevalence in childhood cancer survivors (CCS) than in age-sex-race matched community controls. However, mosaic chromosomal alterations (mCAs), another form of CH with megabase-scale structural alterations (copy gain, copy loss and copy-neutral loss of heterozygosity), have not been examined. Methods: Detection of mCAs was performed on whole-genome sequencing (WGS, 30X) data from 5-year CCS with the Mosaic Chromosomal Alterations (MoChA) caller which utilizes phased genotypes, coverage, and B allele frequency (BAF) at heterozygous sites (HETS). We implemented the pipeline established by the TOPMed consortium to detect low mutant cell fractions (CF ≥1%). Variant filtration criteria: minor allele frequency 1%, the read depth of either allele 5, and only one variant retained in each 1Kb window. Called mCA filtration criteria: 100 HETS; lod score 5; relative coverage 2. 9 or BAF deviation 0. 16 and relative coverage 2. 5. Autosomal mCAs (CF ≥1%, HETS 100 and length 1Mb) retained. Multivariable Cox models evaluated the association between mCAs and specific late-effects including all-cause mortality, obesity, myocardial infarction (MI) or cardiomyopathy (CMP) ; multivariable logistic models evaluated the association between mCAs and childhood cancer diagnoses. All models were adjusted for age, sex and therapeutic exposures. Results: In our evaluation of 4, 330 CCS (median age at blood draw: 26. 8 years) and 433 controls (33. 6 years) with WGS data from the St. Jude Lifetime Cohort, the prevalence of mCAs was slightly higher among CCS than community controls (4. 83% vs. 4. 16%). Among CCS, mCAs were associated with therapeutic exposures (alkylating agents: odds ratio OR=1. 48, 95% CI=1. 09-2. 00; antimetabolites: 1. 53, 1. 02-2. 31; corticosteroids: 0. 60, 0. 40-0. 91). In contrast to recent mCA studies in the general population, we observed no co-occurrence with CH point mutations, and no associations with late-effects including all-cause mortality, obesity, MI or CMP. Interestingly, mCAs were significantly associated with the primary diagnosis of acute myeloid leukemia (AML, OR=2. 86, 95% CI=1. 63-5. 01). Furthermore, this finding was replicated in 2898 5-year survivors from the Childhood Cancer Survivor Study (OR=3. 77, 95% CI=1. 94-7. 33). Conclusion: mCAs were not associated with age-related morbidities and mortality among CCS. However, we identified a striking association between mCAs and previous diagnoses of AML independent of treatment exposures. If validated among AML patients at the time of diagnosis, mCAs, which reflect the underlying genome instability, may serve as a diagnostic biomarker for AML. Citation Format: Xijun Zhang, Na Qin, Qian Dong, Cheng Chen, John Easton, Heather Mulder, Xiang Chen, Kyla Shelton, Cindy Im, Yutaka Yasui, Greg Armstrong, Kirsten K. Ness, Melissa M. Hudson, Paul Auer, Jinghui Zhang, Zhaoming Wang. Increased mosaic chromosomal alterations among survivors of childhood acute myeloid leukemia abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 3954.