645P - WRN mutated colorectal cancer (CRC) is characterized by a distinct molecular and immunological profile

Abstract

BackgroundWerner syndrome gene (WRN) encodes a DNA helicase with an exonuclease activity that contributes to DNA repair. In cancer, WRN mutations lead to genomic instability. It is known that WRN is necessary to sustain in-vivo growth of cancers cells with microsatellite instability (MSI), including CRC. WRN is a very promising new target especially in cancers with MSI. There is still a lack of knowledge about the frequency of WRN alterations and their association with immunological and molecular phenotypes. MethodsTumour samples from 6854 CRC patients were analyzed using NGS (NextSEQ on 592 genes), in-situ hybridization and immunohistochemistry (Caris Life Sciences, Phoenix, AZ, USA). Tumour mutational burden (TMB) was calculated based on somatic non-synonymous missense mutations, and MSI was evaluated by NGS of known MSI loci. ResultsWRN mutations (WRN-mut) were observed in 80 of 6854 samples (1.2%). A higher prevalence of WRN-mut was detected in right- compared to left-sided CRC (2.4% vs 0.7%, p<.0001). In WRN-mut (MT) CRC, TMB (43 vs. 8.6 mutations/megabase [mut/MB], p<.0001) and PD-L1 expression (13% vs 4%, p<.0001) were higher compared to WRN wild-type (WT). A higher frequency of MSI-H was seen in cancers harboring WRN-mut (56% vs 7%, p<.0001). Also, WRN-mut was associated with a higher TMB in both MSI-H subgroup of tumors (54 vs 40 mut/MB, p=.03) and MSS subgroup (43 vs 8.6 mut/MB, p<.0001). Several differences between WRN-mut and WRN-WT CRC was observed, including TP53 (47% vs 73%), KRAS (34% vs 49%), APC (56% vs 73%), BRAF (26% vs 9%), ASXL1 (25% vs 4%), ERBB2 (9% vs 2%), BRCA1 (8% vs 1%), BRCA2 (15% vs 2%), CDK12 (10% vs 1%), (p<.01 for all). Copy number alterations (CNA) of CDX2 were seen only in WRN-WT tumours (6.4% vs 1%, p=.026) and CNAs seen more frequently in WRN-mut tumours included CD274, CALR, CRTC1, ELL, JAK3, KEAP1, LYL1, MEF2B (p<.01). ConclusionsThis is the largest profiling study to investigate the molecular and immunological landscape of WRN-mut CRCs. We show the high prevalence of MSI in WRN-mut tumours and their association with higher TMB and PD-L1 expression. Furthermore, it revealed that WRN-mut CRC is characterized by a distinct genetic profile. Our data might serve to tailor treatment in WRN-mut CRC. Legal entity responsible for the studyThe authors. FundingHas not received any funding. DisclosureAll authors have declared no conflicts of interest.