Abstract 5757: Germline and somatic mutational landscape of Chinese early-onset colorectal cancers

Abstract

Abstract Background: The incidence of colorectal cancer (CRC) in young people, described as early-onset colorectal cancer (EOCRC) has been rising up in decades. Apart from definite familial genetic disease, a considerable proportion of EOCRC remained unknown of the mechanism. Characterizing the difference in genomic features of EOCRC and late-onset CRC (LOCRC) would help us to understand it. Methods: A total of 1777 Chinese CRC patients diagnosed in 2019-2020 were included. 489 patients under 50 years were defined as EOCRC. A 733-gene panel next-generation sequencing (NGS) testing and measurement of tumor mutational burden (TMB) levels based on the panel were conducted in all patients’ tumor specimen. Lynch syndrome (LS) was defined as patients harboring at least one non-benign germline mutation in four LS MMR genes (MLH1, MSH2, MSH6, PMS2). Results: 43 of 489(8.8%) cases and 54 of 1288 (4.2%) cases were MSI-H in EOCRC and LOCRC, separately. Excluded 97 LS patients (84.3% in MSI-H EOCRC and 72.0% in MSI-H LOCRC), the proportion of non-LS MSI-H in EOCRC and in LOCRC were 1.8% and 1.7%, separately. Compared to non-LS MSI-H LOCRC, EOCRC has higher germline mutational frequencies in APC, CD74, ATM, BCL2L11, CHEK2, and RECQL4 genes and somatic mutational frequencies in APC, ERCC4, CHD2, ARHGAP5, CASP8, and ATM genes. In non-LS MSS patients, germline mutations in CHEK2, NBN and POLE genes, somatic SNV/indels in RNF43, ATR, AFF3, JAK2, POLG, CHD2 genes and somatic copy number gain in genes on chromosome 8 (ZNF703, FGFR1, MYC, PTK2) occurred more frequently in EOCRC. KEGG enrichment analysis in somatic mutations indicated significant overexpressed MAPK signaling pathway. The TMB level was significantly lower in non-LS MSS EOCRC than in LOCRC. Conclusions: The proportion of non-LS MSI-H in Chinese EOCRC and LOCRC were approximate. Non-LS MSS EOCRC had marked chromosome 8 somatic copy number gain and MAPK signaling pathway, indicating the potential mechanism. The comparative lower TMB level in EOCRC was concordance with previous studies and the correlations between low TMB level and high CNV burden also corroborate the etiopathogenesis. Citation Format: Xiancheng Zeng, Junhao Liu, Yurong Luo, Hailiang Li, Xinyi Liu, Mengli Huang. Germline and somatic mutational landscape of Chinese early-onset colorectal cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5757.