e14503 Background: Data on the prognostic significance of promoter CpG island methylation in colorectal cancer (CRC) are conflicting, possibly due to associations between methylation and other factors affecting survival such as genetic alterations and use of adjuvant therapy. Here we examine the prognostic impact of promoter methylation in CRC patients treated with surgery alone in the context of microsatellite instability (MSI), BRAF- and KRAS mutations. Methods: 173 CRCs were analyzed for promoter methylation of 19 tumor suppressor- and DNA repair genes, the CpG island methylator phenotype (CIMP), MSI, the exon 15 V600E BRAF mutation and KRAS codon 12 and 13 mutations. Results: Unsupervised hierarchical clustering based on methylation status of 19 genes revealed three subgroups: cluster 1 (CL1, 57% (98/173) of CRCs), cluster 2 (CL2, 25% (43/173) of CRCs) and cluster 3 (CL3, 18% (32/173) of CRCs). CL3 had the highest methylation index (0.25, 0.49 and 0.69 respectively, p=