Abstract 5711: Gene expression profiles in BRAF V600E mutant colorectal cancer and association with SFRP2 methylation status
Authors: Yasui Kazuya , Nagasaka Takeshi , Toshima Toshiaki , Kawai Takashi , Shigeyasu Kunitoshi , Mori Yoshiko , Haraga Junko , Nakamura Keiichiro , Umeda Yuzo , Tazawa Hiroshi , Goel Ajay , Fujiwara Toshiyoshi 
Published: July 2017

Background: Classification of colorectal cancer (CRC) according to gene expression profiling remains controversial with regards to their ability to stratify patients for precision therapy. Several studies have suggested that ‘stem cell like’ or ‘epithelial-mesenchymal transition (EMT)’ signature associates with poor prognosis. Meanwhile CRCs with BRAF V600E mutation have shown poor outcomes in several clinical trials, but the biological roles of BRAF mutation have not been fully elucidated.

Materials and Methods: To evaluate biological roles of BRAF mutations in CRC, we performed mRNA microarray analysis 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. Pathway analyses were performed by Gene Set Enrichment Analysis (GSEA). Following identification of candidate biomarkers that influence poor outcomes and associate with BRAF V600E mutation, we examined 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.

Results: By the GSEA, prominent signatures enriched in CRCs with BRAF V600E mutation vs. wild-type were EMT-related processes (EMT and myogenesis). Additionally, CRC with BRAF V600E mutation strongly associated with inactivation of Wnt signaling and intestinal differentiation-related genes. Among the differentially expressed genes between CRCs with BRAF V600E mutation versus wild-type, Wnt-antagonist, Secreted frizzled-related proteins (SFRPs) were significantly upregulated in CRCs with BRAF V600E mutation. As SFRPs are well known to be inactivated in CRCs by promoter hypermethylation, and up to 80% of CRCs are methylated in the promoter region of the SFRP2 gene, we focused and analyzed SFRP2 promoter methylation status in 782 stage II-IV 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 498 (64.2%) stage II-IV CRCs. 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-years RFS rate were 46.8% vs 72.1%; P = 0.015, Hazard ratio 2.06 [95% CI, 1.12 to 3.69]; P = 0.021).

Conclusion: Our results suggest that SFRP2 methylation status could be a potential prognostic biomarker for stage II-IV CRCs, especially with genetic mutations in the KRAS/BRAF genes.

Citation Format: Kazuya Yasui, Takeshi Nagasaka, Toshiaki Toshima, Takashi Kawai, Kunitoshi Shigeyasu, Yoshiko Mori, Junko Haraga, Keiichiro Nakamura, Yuzo Umeda, Hiroshi Tazawa, Ajay Goel, Toshiyoshi Fujiwara. Gene expression profiles in BRAF V600E mutant colorectal cancer and association with SFRP2 methylation status [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5711. doi:10.1158/1538-7445.AM2017-5711