Demographic and other selected characteristics of non-Hispanic white participants from the Aspirin/Folate Polyp Prevention Study with genotypeand outcome data that were included in the present analysis (see ) are presented in . Among the 792 participants, 370 (46.7%) had a recurrence of one or more colorectal adenomas during follow-up. The mean age was almost 58 years and the majority of participants were males (64%). Approximately 39% of participants had a family history of colorectal cancer among first-degree relatives. On average, participants were followed for 32.8 months from randomization to their follow-up colonoscopy. As observed in the full analyses of the trial (21
), individuals who were randomized to 81 mg/day of aspirin were less likely to have a recurrence compared with those randomized to the placebo arm (P=0.04), whereas treatment with 325 mg/day aspirin (P=0.83) or 1 mg/day folate (P=0.51) was not significantly associated with the outcome. In addition, the main effect of aspirin in this subset of 792 participants (0.77 RR, 0.63–0.94 95% CI, P=0.009 for 81 mg aspirin and 0.99 RR, 0.82–1.19 95% CI, P=0.89 for 325 mg aspirin) was similar to that for the entire cohort (21
Selected characteristics of the study populationa
We first examined associations of common SNPs in the vicinity of the ODC1
gene with risk of adenoma recurrence in single SNP analyses (). The region analyzed encompassed about 23 kb in total: including approximately 7 kb upstream (5’) and 8 kb downstream (3’) of the 8 kb transcribed region of the ODC1
gene. In , minor allele frequencies (MAFs) and gene locations are shown for the SNPs that were included in the statistical analyses, including 15 newly genotyped SNPs and rs2302615, which was genotyped previously (17
). Results for seven SNPs were statistically significant at a value of P < 0.05. Of these, five were associated with increased risk: rs11694911 (1.29 RR, 1.10–1.51 95% CI), rs2430420 (1.17 RR, 1.05–1.31 95% CI), rs10929669 (1.22 RR, 1.04–1.43 95% CI), rs1049500 (1.38 RR, 1.10–1.73 95% CI), rs2357551 (1.13 RR, 1.01–1.27 95% CI); and two were associated with decreased risk: rs13000916 (0.89 RR, 0.80–0.99 95% CI), rs818162 (0.86 RR, 0.76–0.97 95% CI) of adenoma recurrence. After accounting for multiple comparisons using a 20% false discovery rate threshold (Q < 0.2), all seven associations were still statistically significant. The previously investigated SNP, rs2302615, was not associated with risk when the analysis was restricted to non-Hispanic whites, in agreement with our previous results for all participants (17
). Although an additive genetic model was used for all SNPs in the analyses shown in , other models (i.e. dominant or recessive) provided a better fit for several of the SNPs with a significant association suggesting larger effect sizes (data not shown).
Associations of ODC genotypes with risk of adenoma recurrence, Aspirin/Folate Polyp Prevention Study, 1994–2001
We also examined the association of adenoma recurrence with common haplotypes found within 4 linkage blocks identified in this segment of the chromosome (see ) to assess the combined effect of correlated SNPs. In the first block, which contains 3 SNPs, a haplotype (GTG) found in 10.6% of the study population (8.6% controls, 13.0% cases) was associated with a 33% increased risk (1.33 RR, 1.12–1.57 95% CI, P=0.001) of adenoma recurrence (per copy of the haplotype) compared to the most common haplotype in this block (TCG). Another haplotype (GCA), occurring in 24% of the study population (23.1% controls, 25.5% cases), was associated with a 14% increased risk that was borderline statistically significant (1.14 RR, 1.00–1.30 95% CI, P=0.06). A test of the overall association of genetic variation in block 1 with adenoma recurrence was statistically significant (P=0.011). In the second block, which contains 4 SNPs, one haplotype (CCCT) found in 23.3% of individuals (25.2% controls, 21.4% cases) was associated with a 15% decreased risk (0.85 RR, 0.73–0.98 95% CI, P=0.029) and another (GTCC) found in 4.1% of individuals (2.7% controls, 5.7% cases) was associated with a 27% increased risk (1.27 RR, 1.01–1.61 95% CI, P=0.044) compared to the most common haplotype (GCCT). Overall, genetic variation in this block was also statistically significantly associated with adenoma recurrence (P=0.012). Genetic variation in block 3 was not associated with the outcome (P=0.63). For the fourth block, one haplotype (CAAA) found in 26.1% of individuals (23.8% controls, 28.9% cases) was associated with a 17% increased risk (1.17 RR, 1.02–1.33 95% CI, P=0.021) per copy of the haplotype compared to the most common haplotype in this block (GAAG), but the test of overall association was not statistically significant (P=0.19).
Association of ODC haplotypes with risk for adenoma recurrence, Aspirin/Folate Polyp Prevention Study, 1994–2001
Although the tag SNPs analyzed here were not in strong linkage disequilibrium (by definition r2<0.8), some correlation still exists between them. Thus, in addition to the single SNP and haplotype analyses described above, a multiple SNP analysis was used to assess which SNPs in this chromosomal region were independently associated with risk of adenoma recurrence. Starting with all SNPs in , those that were not statistically significantly associated with risk were successively removed from a composite regression model, until only 2 SNPs remained showing statistically significant independent associations with risk: rs11694911 (1.29 RR, 1.08–1.53 95% CI, P=0.005) and rs2430420 (1.20 RR, 1.03–1.40 95% CI, P=0.022) using dominant genetic models (which provided a better fit than additive or recessive models). The joint contribution of these two SNPs to adenoma risk was highly statistically significant (P=0.0003) and the linkage disequilibrium between them was very low (r2 = 0.05). In addition, there was no evidence for an interaction between the two SNPs: their combined effect was essentially the sum of their excess risks. Thus, having at least one risk allele at both loci (15% of the study population) was associated with a 53% increased risk (1.53 RR, 1.24–1.90 95% CI, P<0.001) whereas having at least one risk allele at only one loci (45% of the study population) was associated with a 24% increased risk (1.24 RR, 1.12–1.38 95% CI, P<0.001) compared to having no risk alleles at either loci (40% of the study population, referent group).
Finally, we evaluated whether there was evidence for an interaction between ODC genotypes and aspirin treatment on risk for adenoma recurrence. shows the association of each genotype with adenoma risk stratified by aspirin treatment group. Two SNPs (rs2430420 and rs28362380) had nominally statistically significant interactions, although these findings were not corrected for multiple testing. For rs2430420, which had an independent statistically significant main effect as described above, the variant allele was not associated with risk in the placebo group, but was associated with an increased risk of 21% (1.21 RR, 0.98–1.49 95% CI) and 38% (1.38 RR, 1.15–1.66 95% CI) per allele in the 81 and 325 mg aspirin treatment groups, respectively. Conversely, when the effect of aspirin was stratified by rs2430420 genotype (), 81 mg aspirin treatment appeared to be protective among wild type homozygotes, with a risk reduction of 32% (RR 0.68, 0.50–0.94 95% CI) compared to placebo, but not among heterozygotes/variant homozygotes (RR 0.95, 0.75–1.20 95% CI). Notably, there was no evidence for interaction of aspirin treatment with genotype at the other SNP that was independently associated with risk (rs11694911). However, for rs28362380, which did not have a main effect on risk overall (see ), each variant allele was associated with a 25% risk reduction in the placebo group (0.75 RR, 0.53–1.04 95% CI), a 39% risk increase in the 81 mg/day aspirin treatment group (1.39 RR, 1.02–1.87 95% CI), but virtually no change in risk in the 325 mg/day aspirin treatment group (1.03 RR, 0.80–1.35 95% CI) (). Conversely, when the effect of aspirin was stratified by genotype (), 81 mg aspirin treatment was associated with a 25% risk reduction in wild type homozyzgotes (0.75 RR, 0.61–0.92 95% CI) compared to placebo, but not among heterozygotes/variant homozygotes (1.32 RR, 0.85–2.06 95% CI).
Association of ODC genotypes with risk of adenoma recurrence stratified by aspirin treatment group, Aspirin/Folate Polyp Prevention Study, 1994–2001
Association of aspirin treatment with risk of adenoma recurrence stratified by ODC genotypes, Aspirin/Folate Polyp Prevention Study, 1994–2001
Lastly, although we previously reported a statistically significant interaction between rs2302615 and aspirin treatment (17
), the interaction was not statistically significant in the current analyses which differed from the prior analyses in that they were restricted to non-Hispanic whites, were adjusted for age and sex and analyzed the aspirin treatment groups separately ( and ). However, when we precisely mimicked the previous analysis by assessing the combined aspirin treatment effect (81 and 325 mg doses together) stratified by genotype using a dominant genetic model, the interaction was still not statistically significant although the results were similar (not shown): specifically, in the current analysis, as in the prior analysis, there was no risk reduction in the wild type homozygotes (1.04 RR, 0.83–1.30 95% CI), while a 17% risk reduction was observed among heterozygotes/variant homozygotes (0.83 RR, 0.66–1.04 95% CI, Pint
=0.15) that was only slightly smaller in magnitude than that reported previously (23% risk reduction, 0.77 RR, 0.63–0.95 95% CI, Pint
=0.04, see (17