Phenotypic and tumor molecular characterization of colorectal cancer in relation to a susceptibility SMAD7 variant associated with survival

The minor allele (G) of rs4939827, a SMAD7 (18q21) intronic variant, is associated with a lower risk of developing colorectal cancer (CRC) and poorer survival after diagnosis. Our objective was to evaluate the associations of this variant with different tumor phenotype and intratumoral molecular characteristics. We evaluated 1509 CRC cases and 2307 age-matched controls nested within the Nurses' Health Study and the Health Professionals Follow-up Study. We used the TaqMan assay to genotype rs4939827 and logistic regression to assess the association of rs4939827 with risk of CRC according to different phenotypic and molecular characteristics. We found that the minor allele (G) in rs4939827 (SMAD7, 18q21) was associated with a lower risk of developing tumor stage pT1 or pT2 CRC [multivariate odds ratio (OR), 0.73; 95% confidence interval (CI) 0.62-0.87] but not tumor stage pT3 or pT4 (multivariate OR, 1.07; 95% CI 0.93-1.23, P for heterogeneity = 1.2 x 10(-4)). The association between rs4939827 and CRC also significantly differed by methylation of RUNX3 (P for heterogeneity = 0.005). Among those with CRC, the minor allele (G) in rs4939827 was significantly associated with poorer overall survival (hazards ratio, 1.20; 95% CI, 1.02-1.42). We can conclude that the minor allele (G) of the germline intronic SMAD7 variant rs4939827 is associated with a lower risk of CRC with earlier tumor stage and CRC without methylation of the tumor suppressor RUNX3. These findings suggest that individuals with this SMAD7 variant that develop CRC are more probably to have tumors with greater invasiveness and methylation of RUNX3, which potentially contributes to their poorer observed survival.