Assessing The Utility Of Cell-Free Dna In Identifying Prostate Cancer And Characterizing Tumor Heterogeneity Via Targeted, Whole Exome, And Whole Genome Multi-Region Sequencing

Early cancer diagnosis, especially while the disease is localized and before symptoms appear, results in significantly higher survival rates compared to late-stage diagnosis. At the time of diagnosis, it is also common to find multiple foci within the prostate in men with localized disease. Cell-free DNA (cfDNA) are short DNA fragments released into circulation by dying cells, which may reflect underlying disease biology and simultaneously allow for the identification of genetically distinct tumor subclones. The objectives of this study are to determine if cfDNA concentration can be used to distinguish between healthy individuals from patients with localized or metastatic castration-resistant prostate cancer (mCRPC), and if somatic mutations identified in tumor tissue are detectable in cfDNA. This study included samples from 277 individuals: 41 healthy donors, 112 patients with localized prostate cancer who underwent radical prostatectomy (RP) at UCSF, and 124 mCRPC patients. Whole peripheral blood was collected in EDTA tubes or PAXgene Blood ccfDNA tubes. Blood and matched tissue from adjacent normal seminal vesicles and multiple tumor regions (1-9 samples per patient) were collected from patients undergoing RP. Extraction of cfDNA was performed on double spun plasma using the Qiagen QIAamp Circulating Nucleic Acid Kits. After extraction, the concentration and fragment length distribution were measured with a Bioanalyzer 2100 Instrument. Fifty-seven samples (multiple tumor tissue foci and matched blood) from nine patients with localized disease were subjected to whole exome sequencing, and 22 samples from five patients were subjected to whole genome sequencing. All samples from 14 patients underwent targeted sequencing with a 2.5Mb panel generated via machine learning on TCGA prostate cancer sequence data. Somatic variant calling was performed with Broad Institute9s Terra platform (GATK4/MuTect2) for tumor tissue and with the Curio platform for cfDNA to build consensus sequences leveraging duplex unique molecular tags. To estimate tumor fraction in cfDNA, ichorCNA was used to profile low pass whole genome sequence data. Total cfDNA concentration was able to distinguish between healthy and metastatic (p = 0.001) participants, adjusted for age; and also between localized and metastatic groups (p Citation Format: Emmalyn Chen, Clinton L. Cario, Lancelote Leong, Karen Lopez, Cesar Marquez, Carissa Chu, Patricia S. Li, Erica Oropeza, Imelda Tenggara, Janet Cowan, Jeffry P. Simko, Daniel K. Wells, Robin Kageyama, June M. Chan, Terence Friedlander, Rahul Aggarwal, Felix Feng, Pamela L. Paris, Peter R. Carroll, John S. Witte. Assessing the utility of cell-free DNA in identifying prostate cancer and characterizing tumor heterogeneity via targeted, whole exome, and whole genome multi-region sequencing [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 719.