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Short Communication |
1 Department of Internal Medicine, University of Utah School of Medicine, Salt Lake City, Utah; 2 Division of Epidemiology and Community Health, University of Minnesota School of Public Health, Minneapolis, Minnesota; 3 Kaiser Permanente Medical Research Program, Oakland, California; and 4 Fred Hutchinson Cancer Research Center, Seattle, Washington
Requests for reprints: Martha L. Slattery, Department of Internal Medicine, University of Utah School of Medicine, Salt Lake City, UT 84108. Phone: 801-585-6955; Fax: 801-581-3623. E-mail: mslattery{at}hrc.utah.edu
| Abstract |
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| Introduction |
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Although biologically plausible, few studies have examined associations between polymorphisms of the TCF7L2 gene and cancer. There has been one report of an association with endometrial cancer (6) and another with familial breast cancer (7). Because of the well-documented role of the APC gene in development of colon cancer (5, 8), it is reasonable to hypothesize an association between TCF7L2 and colon cancer. Findings by Folsom and colleagues using data from the Atherosclerosis Risk in Communities Study suggest that an association exists.5 In their study, the TT genotype of the rs7903146 TCF7L2 gene was associated with a >2-fold increased risk of colon cancer (hazard rate ratio, 2.15; 95% CI, 1.27-3.64).
Using data from a large multicenter study of colon cancer, we looked to confirm those associations as well as to determine other colorectal cancer risk factors that might interact with this pathway given their association with insulin-related factors. Factors evaluated include body mass index (BMI) and variants of insulin-related genes. We also evaluate aspirin and nonsteroidal anti-inflammatory drug (NSAID) use because high doses of salicylates have been shown to reverse hyperglycemia, hyperinsulinemia, and dyslipidemia by improving sensitivity to insulin signaling (9) and may therefore modify risk associated with the TCF7L2 polymorphism.
| Materials and Methods |
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65 y were randomly selected from lists provided by the Centers for Medicare and Medicaid Services (formerly Health Care Financing Administration) and controls <65 were randomly selected from driver's license lists. In Minnesota, controls were randomly selected from driver's license lists. Study eligibility and recruitment details of the study have been published previously (10, 11). The current analysis is restricted to subjects who provided a blood sample from which the TCF7L2 polymorphism could be genotyped. The colon cancer study population consists of non-Hispanic white cases (n = 1443) and controls (n = 1834), Hispanic cases (n = 61) and controls (n = 75), and African-American cases (n = 71) and controls (n = 55). Two cases and three controls did not report race.
Trained and certified interviewers collected diet and lifestyle data as previously outlined (12, 13). The referent year for the study was the calendar year
2 y before date of diagnosis (cases) or selection (controls). Information was collected on demographic factors such as age, sex, and study center; diet, physical activity, aspirin and nonsteroidal drug use, and body size; and other lifestyle factors, including medical, family, and reproductive history.
DNA was extracted from blood drawn from study participants. Genotyping of the rs7903146 polymorphism was done using a Taqman assay obtained from Applied Biosystems. Briefly, 20 ng of genomic DNA were assessed in each participant using a reaction containing assay-specific probes and primers and 1x Taqman universal PCR master mix (contains AmpErase UNG, AmpliTaq Gold polymerase, and reaction buffer) in a 5 µL final volume. Control samples representing all possible genotypes were included at four positions in every 384-well tray. Internal replicates representing >1% of the sample set were blinded and included.
We assessed interaction between the rs7903146 TCF7L2 polymorphism and polymorphisms in the insulin-like growth factor-1 gene (CA repeat and rs5742612), insulin-like growth factor–binding protein 3 (rs2854744 and rs2854746), insulin receptor substrate 1 (rs1801278), and insulin receptor substrate 2 (rs1805097) as previously described (14).
Information on tumor characteristics, including disease stage and survival data, was obtained through local cancer registries. Utah and California tumor registries are part of the national Surveillance, Epidemiology, and End Results program, and the Minnesota registry is a member of the Centers for Disease Control and Prevention–funded cancer registry programs. Additionally, we evaluated microsatellite instability (MSI) in tumors as described previously (15).
Statistical Methods
Statistical Analysis System statistical package version 9.1 (SAS Institute) was used to conduct the analyses. We evaluated the distribution of the genotypes by race and compared the TCF7L2 polymorphism to the independent associations of genetic polymorphisms with colon cancer. Multivariate logistic regression models were used to evaluate the associations between colon cancer and TCF7L2 genotypes; multinomial logistic regression models were used to evaluate the associations of tumor characteristics such as MSI and TCF7L2 genotypes. All logistic regression models were adjusted for age at selection or diagnosis, study center, race or ethnicity, sex, BMI (kg/m2), and physical activity. Odds ratios (OR) and 95% confidence intervals (95% CI) are used to report associations obtained from the multivariate logistic regression models. Trend is assessed by comparing the log likelihood of a logistic regression model with the variable of interest, entered as an ordered categorical variable, to the log likelihood of a model without the variable of interest using a
2 test with one degree of freedom. Multivariate logistic regression models were used to evaluate the joint association of outcome with the TCF7L2 polymorphism and aspirin/NSAIDs, BMI, physical activity, insulin receptor substrate 1, insulin receptor substrate 2, insulin-like growth factor-1, and insulin-like growth factor–binding protein 3. Effect modification between genotypes and exposure variables was evaluated by a likelihood ratio test for a multiplicative interaction term in the logistic regression model.
| Results |
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| Discussion |
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Aspirin and use of NSAIDs have been shown to influence colon cancer risk in several disease pathways, including an insulin-related pathway (16, 17) as well as generally reducing the risk of colon cancer (18, 19). High doses of salicylates have been shown to reverse hyperglycemia, hyperinsulinemia, and dyslipidemia in obese rodents by improving sensitivity to insulin signaling (9). In patients with type 2 diabetes, aspirin treatment has been shown to reduce fasting plasma glucose, total cholesterol, C-reactive protein, triglycerides, and insulin clearance; aspirin reduced hepatic glucose production and improved insulin-stimulated peripheral glucose uptake by 20% (20-25). Insulin resistance and diabetes have been hypothesized to be associated with colon cancer (26), and thus, the TCF7L2 polymorphism, which also has been associated with diabetes and insulin sensitivity, plausibly may modulate colon cancer risk. Our findings that aspirin/NSAIDs modulate the association between TCF7L2 and colon cancer are consistent with previous reports on the association between salicylates and insulin. Our data suggest that the influence of the T allele is modified by the use of aspirin and only increases risk in the absence of aspirin/NSAIDs. Our data further suggest that when carrying the T allele aspirin modifies the risk of both MSS and MSI tumors, whereas when carrying the CC genotype aspirin only affects the risk of having a MSI tumor. We did not observe significant interaction between other insulin-related factors analyzed. Although our findings with aspirin/NSAIDs could be from chance because of several comparisons made, all associations evaluated were hypothesized a priori.
Unlike the study of Folsom and colleagues, we did not observe a statistically significant association between the T allele of the TCF7L2 polymorphism overall, although an increased risk was observed in the Utah population. Methodologic differences between the two studies exist, in that our study was a population-based case-control study, and the study previously reported by Folsom5 was based on prospective follow-up of the Atherosclerosis Risk in Communities cohort. Differences in association could exist if the genotype was associated with survival and those most critically ill did not participate in the case-control study. However, we did not observe any differences in survival based on TCF7L2 genotype, suggesting that differences in detected association are not the result of selection bias based on poorer response among those who are most ill. The reasons for these differences may therefore be the result of differences in other characteristics of the population, such as recent use of aspirin/NSAIDs, or unmeasured covariates.
The rs7903146 TCF7L2 polymorphism has been associated with development of type 2 diabetes and with insulin sensitivity and secretion (1, 2, 27, 28). Additionally, TCF7L2 is involved in the Wnt/β-catenin pathway, which is critical to proper functioning of the APC gene involved in colon cancer carcinogenesis (4, 5). Although it is a plausible candidate gene that may be associated with colon cancer, we observed a statistically significant increased risk of colon cancer only among those not using aspirin/NSAIDs; further, in the presence of homozygous C alleles, taking aspirin seems to modify risk of MSI+ tumors rather than MSS tumors, whereas for those with one or two T alleles aspirin seems to modify risk of both MSS and MSI tumors. These results need to be confirmed in other studies.
| Acknowledgments |
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| Footnotes |
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The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
Note: The contents of this manuscript are solely the responsibility of the authors and do not necessarily represent the official view of the National Cancer Institute.
5 Folsom AR,Pankow JS, Peacock JM, Bielenski SJ, Heiss G, Boerwinkle E. Variation in TCF7L2 and increased risk of colon cancer: The AcherosclerosisRisk Communities (ARIC) Study. Diabetes Care 2008 Feb 11. ![]()
Received 10/10/07; revised 11/27/07; accepted 1/30/08.
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