Purpose: The SMAD7 gene was recently identified to be associated with colorectal cancer risk. Smad7 protein is a known inhibitor of TGF-β signalling pathway which has a prominent role in tumorigenesis. MGMT gene regulates the direct damage reversal repair pathway, preventing DNA damage and potential cancer development. This exploratory study aims to investigate the association between SMAD7 (rs4464148, rs4939827) and MGMT (rs12917, rs2308321) genotype variants, and all-cancer incidence.
Methods: Our study population was a sub-cohort of the EPIC-Norfolk study, a prospective cohort of approximately 25,000 men and women aged 40-79. Between recruitment 1993-1997 and follow-up to 2006, 192 incident cases and 1155 non-cases with genotype data were identified. Baseline 7-day food diary and health/lifestyle questionnaire data were analysed.
Results: SMAD7 rs4464148 variant genotype was associated with increased cancer incidence [HR=1.34, 95%CI=1.00-1.80] but no overall association for SMAD7 rs4939827 or MGMT genotypes. Participants with variant genotypes in both SMAD7 SNPs had a higher cancer incidence compared to those without any (HR=2.74, 95%CI=1.10-6.79) (P=0.03; P(trend)=0.01). Amongst the younger age participants (<mean 62 years), SMAD7 rs4464148 variant genotype group had higher HR of 1.71 (95%CI=1.03-2.83) compared to the non-variant genotype group.
Conclusions: These findings suggest that SMAD7 rs4464148 common variant genotype is associated with cancer incidence but not SMAD7 rs4939827, MGMT rs12917 or MGMT rs2308321. A combination of variants of the SMAD7 SNPs may be associated with increased cancer risk in this study population. However, these findings need to be replicated in larger studies and in studies of specific cancer sites.
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