Aberrant activation of canonical Wnt signaling is a hallmark event in colorectal carcinogenesis. The Dickkopf-1 (DKK1) and Secreted Frizzled Related Protein 1 (SFRP1) genes encode extracellular inhibitors of Wnt signaling that are frequently silenced by promoter hypermethylation in colorectal cancer (CRC). These methylation events have been identified as prognostic markers of patient outcome and tumor subtype in several cancers but similar roles in CRC have not been comprehensively examined. In CRC, the microsatellite instability (MSI) subtype associates with favorable disease outcome but the molecular events that are responsible remain poorly understood. Consequently, we quantified promoter methylation status of the Wnt antagonist genes DKK1 and SFRP1 in a large population-based cohort of CRCs from Ontario (n = 549) and Newfoundland (n = 696) stratified by MSI status. We examined the association between methylation status and clinicopathological features including tumor MSI status and patient survival. DKK1 and SFRP1 were methylated in 13 and 95% of CRCs, respectively. In Ontario, DKK1 methylation was strongly associated with MSI tumors after adjustment for age, sex and tumor location [odds ratio (OR) = 13.7, 95% confidence interval (CI) = 7.8-24.2, P < 0.001]. Conversely, SFRP1 methylation was inversely associated with MSI tumors after these adjustments (OR = 0.3, 95% CI = 0.1-0.9, P = 0.009). Similar results were obtained in Newfoundland. There were no independent associations with recurrence-free survival. This is the first large study to identify associations between Wnt antagonist promoter hypermethylation and CRC MSI subtype. These events provide insight into subtype-specific epigenetic mediation of Wnt signaling in CRC.

Purpose African Americans (AAs) have the highest incidence of colorectal cancer (CRC) compared to other US populations and more proximal CRCs. The objective is to elucidate the basis of these cancer disparities. . Experimental design 566 AA and 328 Non-Hispanic White (NHW) CRCs were ascertained in five Chicago hospitals. Clinical and exposure data were collected. Microsatellite instability and BRAF (V600E) and KRAS mutations were tested. Statistical significance of categorical variables was tested by Fisher's exact test or logistic regression and age by Mann-Whitney U test. Results Over a ten-year period, the median age at diagnosis significantly decreased for both AAs (68 to 61; P<0.01) and NHWs (64.5 to 62; P=0.04); more AA patients were diagnosed before age 50 than NHWs (22% vs 15%; P=0.01). AAs had more proximal CRC than NHWs (49.5% vs. 33.7%; P<0.01), but overall frequencies of microsatellite instability, BRAF and KRAS mutations were not different nor were they different by location in the colon. Proximal CRCs often presented with lymphocytic infiltrate (P<0.01) and were diagnosed at older ages (P=0.02). Smoking, drinking, and obesity were less common in this group, but results were not statistically significant. Conclusions Patients with CRC have gotten progressively younger. The excess of CRC in AAs predominantly consists of more proximal, microsatellite stable tumors, commonly presenting lymphocytic infiltrate and less often associated with toxic exposures or a higher BMI. Younger AAs had more distal CRCs than older ones. These data suggest two different mechanisms driving younger age and proximal location of CRCs in AAs.

Diet and lifestyle help mediate colorectal cancer (CRC) risk but the molecular events that mediate these effects are poorly characterized. Several dietary and lifestyle factors can modulate DNA methylation suggesting that they may influence CRC risk through epigenetic regulation of cancer-related genes. The Wnt regulatory genes DKK1 and Wnt5a are important contributors to colonic carcinogenesis and are often silenced by promoter hypermethylation in CRC; however, the dietary contributions to these events have not been explored. To investigate the link between dietary/lifestyle factors and epigenetic regulation of these Wnt signaling genes, we assessed promoter methylation of these genes in a large cohort of Canadian CRC patients from Ontario (n=549) and Newfoundland (n=443) and examined associations to dietary/lifestyle factors implicated in CRC risk and/or DNA methylation including intake of vitamins, fats, cholesterol, fibre, and alcohol as well as BMI and smoking status. Several factors were associated with methylation status including alcohol intake, BMI, and cigarette smoking. Most significantly however, dietary vitamin D intake was strongly negatively associated with DKK1 methylation in Newfoundland (p=0.001) and a similar trend was observed in Ontario. These results suggest that vitamin D and other dietary/lifestyle factors may alter CRC risk by mediating extracellular Wnt inhibition.