Abstract A029: Investigating primary colorectal cancer tumor and liver metastasis clonality through whole exome sequencing of synchronous biopsies

Advanced-stage liver metastatic Colorectal Cancer (CRC) disease remission rates are markedly low, often with less time for life-saving but challenging medical procedures and physically demanding regimens of neoadjuvant chemotherapies. Medical decisions supported by patient-specific genomic information may improve cancer prognosis, long-term remission rates, and overall patient health. Understanding the genomic landscape of liver metastasis with respect to primary tumors can help clinical decision-making that may result in added life years for patients with advanced disease. For unresectable metastatic disease, prediction of the possible targetable mutations of both primary colon tumors and liver metastasis could have an impact on treatment decisions and survival rates. In this study 16 samples were collected from five different CRC patients with cooccurring liver metastases. Whole exome sequencing (WES) was performed on an Illumina Hi-Seq 2000. Samples included primary tumor, tumor micro-environment and metastasis (with one patient undergoing a polypectomy). At the biopsy date, treatment naïve samples allowed observation of the natural genomic makeup. Analysis confirmed 70x average coverage. Data were processed with multiple mapping and variant discovery algorithms. In these samples, a putative driver variant, FAM25C was identified, in addition to observing canonic driver mutations for colorectal cancer such as TP53, APC, KRAS. After variant discovery, microsatellite instability and tumor mutation burden (TMB) analyses were conducted. One patient showed high TMB with almost 10-fold more mutations observed, when compared to other samples. All samples of the High-TMB patient share almost half of the same variants, which can be indicative of early expansion of the major clone. Average probabilistic Jaccard similarity coefficient percentages of somatic variants of only primary CRC tumor and liver metastasis tissues were 41.08% with a standard deviation of 4.05% across all patients. Whole exome sequencing of samples with subsequent analysis of clonal variation between CRC tumors and liver metastasis show different mutational composition trends in dissimilarity to the primary tumor. To understand tumor evolution, phylogenetic analysis was conducted for each patient sample. Although different studies were conducted on understanding the genomic properties of metastasis through pairwise comparison, detailed studies which investigate the genomic patterns of tumor ex