Abstract 2523: Novel genomic characterization in late stage colorectal cancer

Abstract Introduction: Colorectal cancer patients with high-level microsatellite instability benefit more from immune checkpoint inhibitor therapy, but they only account for around 15% of all colorectal cancer patients. The remaining patients are still lack of effective therapeutic biomarkers. For patients in late stage without optimal treatment, it is essential to find novel biomarkers which can be used to select appropriate therapies and therefore improve patients' overall survival. Methods: We used whole-exome sequencing to analyze 114 colorectal cancer samples. The samples included 86 primary late stage tumors and 28 metastatic tumors from liver, lung and other organs. The primary samples were further divided into different groups based on their tumor location (sideness) and microsatellite status (MS) since these indications are of great significance in clinical presentation and treatment. We then assessed somatic genomic lesions, copy number variations, germline gene alterations and mutational signatures in the above three pairs of comparisons respectively (primary vs. metastatic, right- vs. left-sided, MS instable vs. stable). Results: There were significant differences between the analyzed pairs. For the primary and metastatic samples, the most prominent difference was the copy number variation which happened in 25 genes in the metastatic samples and only one gene in the primary samples (gain of IL12) (p = 0.036). For the right- and left-sided comparison, SNP/Indel mutations were the most prominent. They happened more frequently in the right-sided than the left-sided tumors and those are rare genes in colorectal cancer, including BCL11A (p = 0.018), DICER1 (p = 0.038), NR4A3 (p = 0.004), NIN (p = 0.008) and FBXW7 (p = 0.019). For the MSI-MSS comparison, tumor mutation burden (TMB) stands out high in the MSI group compared to the MSS group (p < 0.0001). In addition, dozens of significantly mutated genes were observed in the MSI samples (p < 0.0001), such as KMT2B, ACVR2A, KMT2D, ASXL1, TCF7L2 and etc. However, TP53 occurred mainly in the MSS patients (p = 0.0007). Conclusion: Our study enables a deeper understanding of the genomic characterization of colorectal cancer from an integrated view. Copy number variations, gene mutations, and TMB were found to be the most significant differences between the comparison groups of primary vs. metastatic samples, left vs. right sided samples, and MSI vs. MSS samples respectively. Genomic differences between metastatic and primary samples may be potential therapeutic targets for metastatic colorectal cancer. Citation Format: Jianxia Li, Qianchao Wu, Jianwei Zhang, Huabin Hu, Yue Cai, Jiayu Lin, Jun Liu, Yanhong Deng. Novel genomic characterization in late stage colorectal cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2523.