Introduction
Werner 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.
Materials and Methods
Tumor samples from 6854 CRC patients were analyzed using NGS (NextSEQ on 592 genes), in-situ hybridization and immunohistochemistry (Caris Life Sciences, Phoenix, AZ, USA). Tumor mutational burden (TMB) was calculated based on somatic non-synonymous missense mutations, and MSI was evaluated using a combination of FA, IHC and NGS of known MSI loci.
Results
WRN 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, WRNmut 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 tumors (6.4% vs 1%, p=.026) and CNAs seen more frequently in WRN-mut tumors included CD274, CALR, CRTC1, ELL, JAK3, KEAP1, LYL1, MEF2B (p<.01)
Conclusion
This 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 tumors 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.