Abstract 2509: Analysis of clonal hematopoiesis-associated mutations in the cell-free DNA of advanced cancer patients

Background: Clonal hematopoiesis (CH) is the acquisition of mutations in hematopoietic progenitor cells that can lead to clonal expansion. Recent studies suggest that CH-derived mutations can confound interpretation of cell-free DNA (cfDNA) sequencing results. To better understand the contribution of CH to cfDNA analysis in the metastatic cancer setting, we characterized CH-associated alterations observed in the cfDNA of late-stage cancer patients. Methods: We analyzed somatic variants from cfDNA profiles of over 62,000 patients in four late-stage cohorts: lung (>35,000), gastro-intestinal (>14,000), urogenital (>4,700), breast (>8,600). Matched white blood cell (WBC) and cfDNA was obtained for a subset of patient samples. Plasma cfDNA was processed using a 73-gene (150Kb, Guardant360 TM ) or 500-gene (2Mb, GuardantOMNI TM ) panel and sequenced to average depth of ~5000 molecules, with a 95% limit of detection (LOD) of 0.3-0.4% and 0.15-0.6% variant allele fraction (VAF) for SNVs, and 0.2%-0.7% and 0.4-0.8% for indels (for G360 and OMNI, respectively). Results: In samples processed on the 500-gene panel, DNMT3A, TET2, PPM1D, ASXL1 and SF3B1 were the most frequently mutated CH-associated genes (75% of samples). While the majority (73%) of these mutations were at low variant allele fractions (VAF) of 60,000 samples, JAK2 V617F, a known CH mutation, was observed in 927 samples with VAFs between 0.29% and 98%. Across the combined cohort, we found that in samples with a known CH variant (n=7,717), half of samples had a max CH VAF less than 50% of max tumor VAF. Interestingly, in >25% of samples, the max CH VAF was higher than the max tumor VAF. Initial comparisons of matched plasma and WBC DNA show that 100% (16/16) of clinically relevant and 92% (84/91) of variants of unknown significance (VUSs) across the 73-gene panel were found exclusively in plasma DNA and not in WBC DNA testing. Conclusions: We characterize the distribution of CH mutations across a large number of late-stage plasma samples and show that within highly pre-treated metastatic patients, the VAFs of CH mutations often differ from the tumor and can surpass the level of tumor shedding in circulation. Further investigation of these variants will enable improved understanding of CH in metastatic disease and its differentiation from the circulating tumor DNA. Citation Format: Jennifer Yen, Katie Quinn, Elena Helman, Andrey Chursov, Tracy Nance, Ariel Jaimovich, Kimberly Banks, Aleksandra Franovic, Kristin Gleitsman, John Latham, Arielle Yablonovitch, Marcin Sikora, Stephen Fairclough, Darya Chudova, Richard B. Lanman, AmirAli Talasaz. Analysis of clonal hematopoiesis-associated mutations in the cell-free DNA of advanced cancer patients [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2509.