Supplementary Table 1. Statistical comparisons between the methylation status of the MGMT promoter within colorectal carcinoma (CRC) and clinicopathological features, molecular features of tumors, and rs16906252C>T genotype in cases from the Sydney CRC series. Supplementary Table 2. Statistical comparisons of the methylation status of the MGMT promoter within the colorectal carcinoma (CRC) of cases from the Australasian Colorectal Cancer Family Registry (ACCFR). Supplementary Table 3. Performance of the rs16906252C>T genotype in predicting the MGMT methylation status of the primary CRC of cases from the Sydney and Australasian colon cancer family registry (ACCFR) CRC series. Supplementary Table 4. MGMT methylation in normal tissues of a subset of colorectal cancer cases and healthy controls is associated with the rs16906252C>T variant. Supplementary Table 5. Performance of the rs16906252C>T genotype and presence of lowlevel MGMT methylation in normal tissues of CRC cases in predicting the MGMT methylation status of the primary CRC in a subset of 62 cases from the Sydney CRC series.
ARTICLE ABSTRACT
Purpose: Methylation of the MGMT promoter is the major cause of O6-methylguanine methyltransferase deficiency in cancer and has been associated with the T variant of the promoter enhancer SNP rs16906252C>T. We sought evidence for an association between the rs16906252C>T genotype and increased risk of developing a subtype of colorectal cancer featuring MGMT methylation, mediated by genotype-dependent epigenetic silencing within normal tissues.Experimental Design: By applying a molecular pathologic epidemiology case–control study design, associations between rs16906252C>T and risk for colorectal cancer overall, and colorectal cancer stratified by MGMT methylation status, were estimated using multinomial logistic regression in two independent retrospective series of colorectal cancer cases and controls. The test sample comprised 1,054 colorectal cancer cases and 451 controls from Sydney, Australia. The validation sample comprised 612 colorectal cancer cases and 245 controls from the Australasian Colon Cancer Family Registry (ACCFR). To determine whether rs16906252C>T was linked to a constitutively altered epigenetic state, quantitative allelic expression and methylation analyses were performed in normal tissues.Results: An association between rs16906252C>T and increased risk of developing MGMT-methylated colorectal cancer in the Sydney sample was observed [OR, 3.3; 95% confidence interval (CI), 2.0–5.3; P < 0.0001], which was replicated in the ACCFR sample (OR, 4.0; 95% CI, 2.4–6.8; P < 0.0001). The T allele demonstrated about 2.5-fold reduced transcription in normal colorectal mucosa from cases and controls and was selectively methylated in a minority of normal cells, indicating that rs16906252C>T represents an expression and methylation quantitative trait locus.Conclusions: We provide evidence that rs16906252C>T is associated with elevated risk for MGMT-methylated colorectal cancer, likely mediated by constitutive epigenetic repression of the T allele. Clin Cancer Res; 22(24); 6266–77. ©2016 AACR.
