Colorectal cancers (CRC) with BRAF V600E mutations have typically shown poor outcomes in several clinical trials, but its biological role has not been fully elucidated. Classification of CRCs according to gene expression profiling and methylome analysis remains controversial with regards to their ability to stratify patients for precision therapy.
We performed mRNA microarray analysis and used pathway analyses by Gene Set Enrichment Analysis (GSEA) in the following three subsets; eight BRAF-mutant CRC tissues without MSI, six BRAF-mutant CRCs with MSI and five BRAF-wild type CRCs with MSI. Following identification of candidate biomarkers that affect poor outcomes and associate with BRAF V600E mutation, we examined epigenetic variations of these candidate biomarkers in a cohort of 1068 CRC patients who underwent surgical resection of their primary tumor and/or metastatic lesions from 1994 to 2015 at the Okayama University Hospital.
Prominent signatures enriched in CRCs with BRAF V600E mutation were EMT-related processes (EMT and myogenesis), Wnt signaling and intestinal differentiation-related genes. Among the differentially expressed genes, Wnt-antagonist, Secreted frizzled-related proteins (SFRPs) were significantly upregulated in CRCs with BRAF V600E mutation especially without MSI. As SFRPs are well known to be inactivated by promoter hypermethylation, and up to 80% of CRCs are methylated in the promoter region of the SFRP2 gene, we speculated and analyzed SFRP2 promoter methylation status in 993 CRCs of our cohort by a modified highly sensitive assay for bisulfite DNA followed by fluorescence-based PCR, as we previously reported (JNCI 2009). SFRP2 methylation was observed in 647 (65.2%). Interestingly, SFRP2 unmethylated CRCs with genetic mutation in the KRAS/BRAF genes demonstrated significantly poorer outcome in RFS compared with SFRP2 methylated CRCs with genetic mutations in the KRAS/BRAF genes (5-yrs RFS: 59.0% vs 80.4%, P
Our results suggest that SFRP2 methylation status could be a potential prognostic biomarker for CRCs, especially with genetic mutations in the KRAS/BRAF genes.
Clinical trial identification
Legal entity responsible for the study
Department of Gastroenterological Surgery, Okayama University
All authors have declared no conflicts of interest.