20q amplification defined by genomic and clinical characteristics as a subgroup with increased prevalence and better survival in metastatic colorectal cancer.

Abstract

e16003 Background: Genomic instability from 20q amplification is an oncogenic pathway in colorectal cancer (CRC). Several genes have been implicated, including BCL2L1, AURKA, SRC, ASXL1, GNAS and TOP1. There is a lack of data regarding 20q amplified group and one study implicating these genes suggested these patients have better overall survival. Next Generation Sequencing (NGS) has become widely used in metastatic CRC (mCRC) and easily identifies patients with 20q amplification. Nevertheless, most oncologists do not routinely consider 20q amplification status and this subgroup remains underinvestigated. This study aims to investigate genomic and clinical characteristics of 20q amplified mCRC using a single-center retrospective cohort and a multi-center genomic dataset. Methods: A cohort was identified comprising patients with mCRC who had NGS testing of tumor DNA and were treated between 2014-2019. Cases with and without 20q amplification were identified. Genomic, clinical and survival data were analyzed. Significant genomic findings were compared with all-stage CRC data using the AACR Genomic Evidence Neoplasia Information Exchange (GENIE) and The Cancer Genome Atlas (TCGA) databases. Results: Of the mCRC cohort ( n= 72), 15% ( n= 11) had 20q amplification. Amplified and non-amplified groups had no significant differences in age, sex or follow-up time. Patients with 20q amplification were more likely to have never smoked, and less likely to have treatment with targeted therapy. Survival analysis showed clear separation with longer overall survival for the amplified group. Eight genes at loci 20q11 to 20q13 were amplified - in order of frequency: ASXL1, GNAS, ARFRP1, ZNF217, AURKA, BCL2L1, SRC and TOP1. 20q amplification was significantly associated with wild-type RAS and BRAF, microsatellite stability, mutant TP53 and mutant APC. Using the GENIE and TCGA databases, it was found that metastatic disease had increased prevalence of all 20q amplified genes except TOP1, when compared to all-stage CRC. Conclusions: Clinical use of NGS identifies the 20q amplification subgroup that has increased prevalence in mCRC (compared to all CRC). Compared to non-20q amplified mCRC, this group had better survival, suggesting genomic pattern in mCRC is a novel independent prognostic marker. We believe mCRC patients would benefit from further studies defining a genomic prognostication model and development of therapy targeting the 20q amplification pathway.