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Carcinogenesis Advance Access originally published online on October 17, 2007
Carcinogenesis 2007 28(12):2575-2580; doi:10.1093/carcin/bgm229
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© The Author 2007. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org

MSH2 –118T>C and MSH6 –159C>T promoter polymorphisms and the risk of colorectal cancer

Miralem Mrkonjic1,2,3, Stavroula Raptis1,2,3, Roger C. Green4, Neerav Monga5, Darshana Daftary5, Elizabeth Dicks6, H.Banfield Younghusband4, Patrick S. Parfrey7, Steven S. Gallinger2,8,9, John R. McLaughlin2,10,11, Julia A. Knight2,10,11 and Bharati Bapat1,2,3,*

1 Department of Pathology and Laboratory Medicine, Mount Sinai Hospital, Toronto, Ontario M5T 3L9, Canada
2 Samuel Lunenfeld Research Institute, Mount Sinai Hospital, Toronto, Ontario M5T 3L9, Canada
3 Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, Ontario M5G 1L5, Canada
4 Department of Genetics, Memorial University, St John's, Newfoundland A1B 3V6, Canada
5 Ontario Familial Colorectal Cancer Registry, Cancer Care Ontario, Toronto, Ontario M5G 2L7, Canada
6 Faculty of Medicine, Memorial University, St John's, Newfoundland A1B 3V6, Canada
7 Department of Clinical Epidemiology, Memorial University, St John's, Newfoundland A1B 3V6, Canada
8 Department of Surgery, Mount Sinai Hospital, Toronto, Ontario M5G 1X5, Canada
9 Department of Surgery, University of Toronto, Toronto, Ontario M5G 1L5, Canada
10 Prosserman Centre for Health Research, Mount Sinai Hospital M5T 3L9, Toronto, Ontario, Canada
11 Department of Public Health Sciences, University of Toronto, Toronto, Ontario M5T 3M7, Canada

* To whom correspondence should be addressed. Tel: +416 586 4800 ext. 5175; Fax: +416 361 2655; Email: bapat{at}mshri.on.ca


   Abstract
Top
 Abstract
Introduction
 Materials and methods
 Results
 Discussion
 Supplementary material
 Funding
 References
 
The most important indicator of colorectal cancer (CRC) risk is the presence of family history of the disease. Inherited genetic changes, such as single nucleotide polymorphisms, in key candidate genes may contribute to CRC risk. We investigated whether promoter polymorphisms in DNA mismatch repair (MMR) genes MSH2 and MSH6 are associated with the risk of CRC. We genotyped 929 CRC patients and 1098 control subjects from Ontario, and 467 patients and 344 controls from Newfoundland and Labrador, for two promoter polymorphisms in the MMR genes MSH2 and MSH6 using the fluorogenic 5' nuclease assay. We used unconditional logistic regression to evaluate the association between each polymorphism and CRC after adjusting for age and sex. The associations between polymorphisms and tumor clinicopathological features were evaluated with a Pearson's chi-squared test or Fisher's exact test. All statistical tests were two sided. We observed strong associations between the MSH2 –118T>C polymorphism and family history of CRC based on the Amsterdam criteria I (P = 0.005) and Amsterdam criteria I and II (P = 0.036) among cases from Ontario. This association was especially evident among female CRC patients in Ontario (for Amsterdam criteria I, and I and II combined, P = 0.003 and P = 0.0001, respectively). The MSH2 –118T>C polymorphism was associated with strong family history of CRC in Ontario patients.

Abbreviations: CRC, colorectal cancer; HNPCC, hereditary non-polyposis colorectal cancer; MMR, mismatch repair; MSI, microsatellite instability; MSI-H, high-frequency MSI; PCR, polymerase chain reaction; SNP, single nucleotide polymorphism


   Introduction
Top
 Abstract
 Introduction
Materials and methods
 Results
 Discussion
 Supplementary material
 Funding
 References
 
Colorectal cancer (CRC) is the second leading cause of cancer-related deaths in the Western world, affecting ~5% of the general population (1,2), and provides an excellent model for cancer research because of its distinct progression from early adenoma to carcinoma (3). Germline mutations in mismatch repair (MMR) genes are responsible for hereditary non-polyposis colorectal cancer (HNPCC) or Lynch syndrome, a CRC susceptibility syndrome that accounts for ~2 to 3% of all CRCs (4,5). Over 300 mutations have been identified in the MSH2, MLH1 and MSH6 genes; the majority of these mutations result in inactivation of the MMR system (6). These DNA alterations are distributed throughout the genes and consist of nonsense and frameshift mutations, as well as missense alterations.

The DNA MMR system garners great responsibility in guarding the integrity of the genome (7). MMR contributes ~1000-fold to the overall fidelity of DNA replication, targeting mispaired bases and insertion–deletion loops occurring during replication, homologous recombination or as a result of DNA damage (7). The key proteins involved in MMR are as follows: MLH1, MSH2, MSH6 and PMS2. MMR begins with the recognition of mispaired bases by either of the two heterodimeric complexes: MSH2–MSH6 (MutS{alpha}), which recognizes base–base mispairs and insertion–deletion loops, or MSH2–MSH3 (MutSβ), which only recognizes insertion–deletion loops (8,9). A second protein complex, MLH1–PMS2 (MutL{alpha}), binds MutS{alpha} or MutSβ and recruits additional proteins required for the repair, such as HEX1 (Exo1), PCNA, RPA and Pol{delta} (10). The loss of this normal MMR function leads to microsatellite instability (MSI), a type of genomic instability characterized by alterations in the length of microsatellite sequences distributed throughout the genome (9,11).

Up to 30% of CRC cases are associated with variable family history of CRC (11). Among these, known mutations in HNPCC only account for some of the familial risk, and it is possible that some of the remaining familial risk results from common variant alleles with low to moderate penetrance in key candidate genes already associated with CRC (12,13). Many genetic changes in the form of single nucleotide polymorphisms (SNPs) have been identified in the MMR genes, but the function of these SNPs is largely unknown. Such alterations in MMR genes may have various effects on tumor phenotype, depending on where the alteration is located within the gene. In addition, these common missense alterations in MMR genes may not be pathogenic enough to cause CRC individually, but they may affect the levels of gene expression required by the specific cell types to perform normal function (14).

Our main objective is to investigate the contribution of MMR gene polymorphisms to CRC. Since low-penetrance alleles in key candidate genes could influence cancer phenotype and prognosis, we also investigated their associations with clinical and pathological tumor characteristics among the case populations. We previously investigated a panel of five SNPs in the MMR genes MLH1 and MSH2, and their contribution to CRC in two case–control studies (15). We found that the MLH1 –93G>A promoter polymorphism increases the risk of microsatellite unstable [MSI high (MSI-H)] CRC in both study populations (15). In this current study, we have examined promoter SNPs in two MMR genes, one in the MSH2 gene, MSH2 –118T>C, and one in the MSH6 gene, MSH6 –159C>T, and investigated their contribution to CRC.

The MSH2 –118T>C polymorphism is located in the core promoter region, 118 nucleotides upstream of the transcription start site in a potential transcription factor binding site (16). The MSH6 –159C>T polymorphism is located 159 nucleotides upstream of the transcriptional start site in a Sp1 transcription factor binding site that is conserved in the MSH6 gene in multiple species including mouse, guinea pigs and Mycobacterium tuberculosis (17). Both of these polymorphisms have potential to affect their respective gene transcriptions to some level and thus make good candidates for low-penetrant alleles that contribute to CRC.


   Materials and methods
Top
 Abstract
 Introduction
 Materials and methods
Results
 Discussion
 Supplementary material
 Funding
 References
 
SNP selection criteria
The two polymorphisms examined in this study were selected on the basis of extensive database and literature searches as described previously (15). Briefly, we selected validated SNPs that were located in the functional domains and gene regulatory regions, with a minor allele frequency >1%, having multiple independent submissions in the SNP databases and/or multiple citations in the literature, that were confirmed by frequency assessment or genotype data, and in which all alleles had been observed in at least two chromosomes.

Study subjects
We conducted these case–control studies with subjects from two different populations, those from the province of Ontario and those from the province of Newfoundland and Labrador (hereafter referred to as Newfoundland). Cases and controls were accrued as described previously (15). Briefly, cases and controls from the Ontario population were obtained from the Ontario Familial Colorectal Cancer Registry. A total of 929 Caucasian cases, aged 20–74 years and diagnosed during the years 1997–2000, were identified for this study. Family history was collected by mailed questionnaires and was used to construct pedigrees. Patients were subsequently classified by his/her family risk. Additional risk factor information was collected from two other mailed questionnaires and blood and tissue specimens were obtained after informed written consent was provided. The protocols were approved by the research ethics boards of Mount Sinai Hospital and the University of Toronto. No cases with familial adenomatous polyposis were included in the registry.

In Ontario, population controls that had not been diagnosed with CRC were accrued through the random selection of residential telephone numbers during the years 1999–2000 and by the use of population-based Tax Assessment Rolls of the provincial government for the year 2000 (18,19). For this study, 1098 Caucasian controls were accrued from the Ontario's registry.

The accrual pattern followed by the Newfoundland Familial Colorectal Cancer Registry was similar to that followed by the Ontario Familial Colorectal Cancer Registry. A total of 467 Caucasian CRC patients younger than 75 years, and diagnosed during the years 1999–2003, were identified from the Newfoundland tumor registry for this study. The recruitment of 344 Caucasian population controls that had not been diagnosed with CRC in Newfoundland was achieved through random-digit dialing.

Control subjects from both provinces were frequency matched to cases by sex and 5-year age group. The mean age for controls from both provinces was calculated from the date of completion of the family history questionnaire, and mean age for the cases was calculated using the age at diagnosis. Cases from both provinces were stratified by family risk according to the Amsterdam criteria I and II (20,21), as described previously (15). We collected data on tumor MSI status, tumor location, tumor stage and tumor grade when available and results from the immunohistochemical evaluation of MLH1 and MSH2 through review of pathological and/or surgical reports. Tumors were staged and graded according to the guidelines set by the American Joint Committee on Cancer (22). Immunohistochemical analysis was performed as described previously (23).

Molecular genetic analysis
SNP genotyping.
Genomic DNA was extracted from peripheral blood lymphocytes using phenol–chloroform or the Qiagen DNA extraction kit (Qiagen, Montgomery County, MD) as reported previously (15). The 5' nuclease polymerase chain reaction (PCR) assay, or the TaqMan® assay (24), was used to genotype the two promoter SNPs in the MSH2 and MSH6 genes. The sequences of the primers and probes are listed in supplementary Table I available at Carcinogenesis online.

MSH2 –118T>C and MSH6 –159C>T were genotyped using Eurogentec qtPCR mix (Eurogentec, San Diego, CA). The PCR conditions for both SNPs and master-mix concentrations are listed in supplementary Table II available at Carcinogenesis online. All assays were run in 96-well polypropylene plates (Axygen Scientific, Union City, CA) and the results were analyzed using the Applied Biosystems 7900HT Sequence Detection System and the accompanying software, SDS versions 2.0 and/or 2.1 (Applied Biosystems, Foster City, CA). Independent quality control for genotyping was done on 5–10% of samples by sequencing (25,26).

TumorMSI analysis.
MSI analysis was performed as described previously (15,26). Briefly, paraffin-embedded colorectal tumor tissue of incident cases, and normal tissue from the same patient, were microdissected in areas with >70% cellularity in tumor and normal cell populations, respectively. MSI analysis was carried out using five or more microsatellite markers from the National Cancer Institute recommended panel of 10 microsatellite markers; these consist of mononucleotides BAT-25, BAT-26, BAT-40 and BAT-34C4; dinucleotides D2S123, D5S346, ACTC, D18S55 and D10S197 and one penta–mono–tetra compound marker, MYC-L (28). The presence of altered or additional bands that resulted from the tumor PCR amplified product, when compared with the matched normal colon PCR product, indicated MSI. MSI status was assigned as MSI-H (≥30% unstable markers among all markers tested), MSI low (<30% markers unstable) or microsatellite stable as per National Cancer Institute recommended guidelines for MSI testing (28). MSI low and microsatellite stable groups were combined into one group, hereafter referred to as simply ‘microsatellite stable or low-frequency MSI’, for analysis purposes. Primer sequences and PCR amplification conditions have been described previously (15).

Statistical analysis
The association of each promoter SNP with CRC incidence, as well as with the age at onset, MSI status, tumor location, tumor grade and stage and family risk status (Amsterdam criteria I and II) were evaluated using Pearson's chi-squared test or Fisher's exact test. Unconditional logistic regression was also used to evaluate the association between each SNP and CRC adjusting for age and sex. All analyses were performed with SAS version 9.0 (SAS Institute, Cary, NC). All statistical tests were two sided. A P value of <0.05 was considered to be of significance, and the results were adjusted using the Bonferroni correction method for multiple comparisons.


   Results
Top
 Abstract
 Introduction
 Materials and methods
 Results
Discussion
 Supplementary material
 Funding
 References
 
CRC patients and population controls
We genotyped a total of 928 cases and 1092 controls for the MSH2 –118T>C and 926 cases and 1093 controls for the MSH6 –159C>T in Ontario, and a total of 467 cases and 344 controls for the MSH2 –118T>C and 463 cases and 344 controls for the MSH6 –159C>T in Newfoundland. The mean ages (mean ± standard deviation) at diagnosis for CRC cases in Ontario and Newfoundland were 59.8 ± 9 years and 60.4 ± 9 years, respectively. The age at diagnosis, family history and clinical and pathological feature distributions for all cases enrolled in this study from both provinces are shown in Table I. Overall, no differences were observed in the distribution of characteristics between the case populations from the two provinces. The mean ages (mean ± standard deviation) of controls from Ontario and Newfoundland were 63.7 ± 9 years and 60.5 ± 9 years, respectively. In both provinces, no differences in age or sex distributions between cases and controls were observed.


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  		Table I. Distribution of age, family history and clinicopathological features of Ontario and Newfoundland CRC patients

 
Distributions of genotypes and alleles
The variant allele frequencies of the MSH2 –118T>C SNP for the Ontario cases and controls were 14.0 and 13.9%, respectively. In Newfoundland, the variant allele frequencies of MSH2 –118T>C SNP for the cases and controls were 14.3 and 12.5%, respectively. For the MSH6 –159C>T SNP, the variant allele frequencies for the Ontario cases and controls were 9.9 and 11.0%, respectively, whereas for the Newfoundland cases and controls, the frequencies were 12.9 and 10.6% respectively. In both provinces, each SNP examined was in Hardy–Weinberg equilibrium among the control populations. Generally, the variant allele frequencies were similar between the cases and controls in both Ontario and Newfoundland. Additionally, we did not observe statistically significant differences in allele frequencies between the general populations, represented by the control subjects, of Ontario and Newfoundland (data not shown).

The distribution of genotypes for the MSH2 –118T>C and the MSH6 –159C>T among cases and controls is shown in Table II. We found no differences in genotype frequency distribution between all cases and all controls within each province.


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  		Table II. Adjusted odds ratio estimates and 95% confidence intervals for the association of MSH2 and MSH6 promoter SNPs with all CRCs in Ontario and Newfoundland

 
Because low-penetrance alleles may not only be associated with cancer incidence but may also influence cancer phenotype and prognosis, we examined associations between available clinical and pathological tumor features among cases and the variant alleles for the two SNPs. For the MSH6 –159C>T polymorphism, we found no association between the SNP variant allele and any of the clinicopathological characteristics in cases from either Ontario or Newfoundland (supplementary Tables III and IV are available at Carcinogenesis online).

In an analysis of Ontario patients with a strong family history, as defined by the Amsterdam I (20) and/or Amsterdam II criteria (21), we found a strong statistically significant association between the MSH2 –118T>C variant C allele and family history of CRC (for Amsterdam I, P = 0.005 and for Amsterdam I and II, P = 0.036) (Table III). Only the association of the MSH2 –118T>C polymorphism with patients meeting the Amsterdam I criteria remained statistically significant after Bonferroni correction for multiple comparisons. A similar association between the MSH2 –118T>C variant and family history (based on Amsterdam criteria) was not observed among Newfoundland cases. Tumor location, tumor MSI, histologic grade and tumor node metastasis stage of the tumors were not associated with the MSH2 –118T>C variant C allele among the Ontario and Newfoundland patients. To prevent the potential confounding effects of MLH1 promoter methylation and to capture the role of the MSH2 –118T>C polymorphism in CRC more accurately, we have additionally removed all CRC patients who are lacking MLH1 expression based on immunohistochemical analysis (n = 74 in Ontario and n = 29 in Newfoundland). A strong statistically significant association between the MSH2 –118T>C variant C allele and family history of CRC with MLH1-proficient CRC patients (for Amsterdam I, P = 0.001 and for Amsterdam I and II, P = 0.011, data not shown) remained, although the latter association was still not significant after Bonferroni correction for multiple comparisons.


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  		Table III. Association of MSH2 –118T>C polymorphism with clinicopathological features of CRC in Ontario

 
Interestingly, for the MSH2 –118T>C promoter SNP, we observed that male patients were significantly or borderline significantly more likely to carry the variant allele compared with female patients in both Newfoundland and Ontario (P = 0.015 and P = 0.05, respectively, Tables III and IV, and stayed significant for MLH1-proficient patients, P = 0.025 and P = 0.044, data not shown). However, both of these results did not remain statistically significant after Bonferroni correction for multiple corrections. There were no such differences in the two control populations.


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  		Table IV. Association of MSH2 –118T>C polymorphism with clinicopathological features of CRC in Newfoundland

 
Since there was some evidence of sex differences between the genotype distributions among cases, we decided to examine the clinical and pathological tumor characteristics by each sex. In Ontario, no associations were observed between the MSH2 –118T>C SNP and clinicopathological features for male CRC patients (supplementary Table V is available at Carcinogenesis online). However, strong associations between the MSH2 –118T>C SNP and female patients from Ontario meeting just the Amsterdam I criteria (P = 0.003) and both Amsterdam I and II criteria (P = 0.0001) were observed (Table V). These associations were also observed in MLH1-proficient female CRC patients (P = 0.001 and P = 0.003, respectively; Table VI). Both of these associations remained significant after Bonferroni correction for multiple comparisons. Additionally, there was a trend toward significance between the MSH2 –118T>C SNP and MSI-H tumor status of female patients in Ontario (P = 0.08, Table V, and P = 0.06 in MLH1-proficient female patients, Table VI). There were no sex-specific associations between the MSH2 –118T>C polymorphism and clinicopathological tumor features in Newfoundland (supplementary Tables VI and VII are available at Carcinogenesis online) even after the MLH1-deficient patients were removed (data not shown).


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  		Table V. Association of MSH2 –118T>C polymorphism with clinicopathological features of female CRC in Ontario

 


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  		Table VI. Association of MSH2 –118T>C polymorphism with clinicopathological features of MLH1-proficient female CRC in Ontario

 

   Discussion
Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
Supplementary material
 Funding
 References
 
Promoter polymorphisms have the potential to regulate gene transcription and affect gene expression. As such, in this study, we describe a large-scale case–control analysis of two promoter SNPs in the highly conserved MMR genes and their association to CRC in two independent populations. Among Ontario cases, a statistically significant association was found between the MSH2 –118T>C promoter variant allele and a strong family history of CRC, as defined by the Amsterdam criteria (20,21). Upon further investigation, we found that this association is seen only in the female CRC patient population and no such association is seen for male patients. This association was not observed in the Newfoundland patients, perhaps because of the small number of patients meeting the Amsterdam criteria and also being carriers of the variant C allele in this study. Independent of sex, the MSH2 –118T>C variant allele and its association with tumor location, tumor MSI, histological grade and tumor node metastasis stage did not reveal any associations in the Ontario and Newfoundland cases (note that tumor node metastasis stage was not available for Newfoundland cases at the time of analysis). We also did not observe any associations between the MSH6 –159C>T SNP and any clinicopathological features examined. Despite the strong functional effects on the MSH6 promoter activity, the MSH6–159C>T polymorphism was not associated with CRC or with any clinical or pathological tumor features. Perhaps more dramatic reduction in MSH6 levels is needed to affect MMR.

As there were many statistical tests performed, some significant results could have occurred by chance, and so the Bonferroni correction method for multiple comparisons was applied. The major finding of this study, the association between the MSH2 –118T>C SNP and strong family history of CRC in female patients of Ontario (based on Amsterdam criteria) was significant even after Bonferroni correction method for multiple comparisons. The other finding in our study, the association between the MSH2 –118T>C SNP and sex was not significant after Bonferroni correction. However, this latter association was observed in two independent populations, indicating that this may not have occurred by chance. A study with a larger sample size is needed to confirm this finding.

We did not observe an association of MSH2 –118T>C polymorphism and family history in Newfoundland. The number of CRC patients meeting Amsterdam I criteria was very small due to the overall smaller sample size; however, there is another factor that may have played a role. Newfoundland is a founder population (29) with the highest rate of CRC in Canada (30); 31% of all CRC cases in Newfoundland have a first-degree relative affected with CRC (30). Many of these families have a large number of HNPCC-related cancers segregating in a pattern consistent with an autosomal dominant mode of inheritance, but have failed to meet the Amsterdam criteria due to the late onset of the cancers (23). Therefore, the Amsterdam criteria may not be the most appropriate classification system to determine the high familial risk of CRC in patients from Newfoundland. Indeed, we did not observe any associations with patients meeting the Amsterdam criteria in our earlier study with the MLH1 –93G>A polymorphism even when we saw such associations with Ontario patients (15). In addition, only 40% of Newfoundland families meeting the Amsterdam criteria have MMR-deficient tumors (30). The other 60% would therefore be defined as familial CRC type X syndrome (30,31). Thus, the proportion of families with familial CRC type X is higher in Newfoundland (60%) than those reported in other populations (40%) (30).

The frequencies of the polymorphic alleles are known to vary by ethnic backgrounds (32). The frequency of the MSH2 –118T>C variant C allele in the general populations of Ontario and Newfoundland were 13.8 and 12.5%, respectively; both values are lower than those published in Asian populations—20% in Japanese and Korean populations (16,33). The differences between our study populations, which are Caucasian, and the reported Asian populations are not surprising, and we have observed these differences for other MMR polymorphisms examined in our previous study (15). In the Korean population, the MSH2 –118T>C SNP was examined in a small subset of HNPCC patients (n = 40), suspected HNPCC patients (n = 56) and early-onset CRC patients (n = 40), and 157 control subjects. Consistent with our findings, no differences in variant allele frequencies between CRC cases and controls were observed in this study (16). Similarly, the contribution of the MSH2 –118T>C SNP to lung cancer was also examined in another Korean case–control population with no significant results (34).

Functional studies have shown that the MSH2 promoter region beginning 300 nucleotides upstream of the transcription start site is crucial for the transcription of the MSH2 gene (16,33). The MSH2 –118T>C polymorphism is located in a NF-Y (also called CBF or CAAT-binding factor) transcription factor binding site (33). NF-Y is a known estrogen-responsive element (35–38). The variant C allele creates an AP1 transcription factor binding site and the AP1 is activated by antiestrogens (like androgens) in the presence of estrogen receptor-beta, which is expressed in the gastrointestinal tract (33,39). Estrogen was found to up-regulate MSH2 gene transcription and increase MMR activity in endometrial cells (40); however, the exact mechanism of this up-regulation is unknown. Estrogen has a protective effect in CRC as it reduces the risk of MSI-H CRCs while its withdrawal increases the risk of MSI-H tumors (41). Taken together, the evidence presented in these studies could indicate a role for the MSH2 –118T>C polymorphism that could involve altering the responsiveness of the MSH2 promoter to estrogen. Additionally, MLH1 was also found to be up-regulated by estrogen (40) and the MLH1 promoter is primarily regulated by the NF-Y transcription factor (42). These findings may explain why the MSH2 –118 variant C allele is associated with a strong family history of CRC, as defined by Amsterdam criteria, in female CRC patients and shows a trend toward association with MSI-H tumor phenotype. The MSH2 –118 variant C allele would eliminate the protective effects of estrogen, as it abolishes the binding of the estrogen-responsive element to the MSH2 promoter. Additional investigations are required to define the exact role of this MSH2 –118T>C variant.

The MSH2 –118T>C is not the first polymorphism to show sex-related differences in CRC risk. A promoter polymorphism in the MDM2 gene, SNP309 (T>G), was shown to increase the risk of CRC, as well as other cancers, in women only (43,44). It is believed that the SNP309 variant G allele increases the affinity of an estrogen-responsive SP1 transcription factor and, thus, up-regulates the transcription of the MDM2 gene (44,45). MDM2, in turn, attenuates the p53 pathway affecting cell-cycle arrest, DNA repair, cellular senescence and apoptosis, and increases the risk for tumorigenesis. It seems that the p53 and MSH2 pathways have sex-specific, hormone-dependent roles.

In this study, we found the MSH2 –118T>C polymorphism to be associated with clinical family history in women. It is possible that this SNP plays a role in the MSH2 response to sex hormones, since MSH2 expression is enhanced by the sex hormones in particular tissues (39). Unfortunately, this polymorphism has not received much attention, as there is only one study, to date, which examines the effects of the MSH –118T>C in lung cancer (33). It would be interesting to examine the role of this polymorphism in sex-specific cancers, such as endometrial, ovarian and prostate cancers. Further characterization of promoter polymorphisms and the cumulative effects that such alterations have on gene expression and ultimately disease risk may lead to new insights into the contribution of low-penetrant alleles to cancer incidence and progression.


   Supplementary material
Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 Supplementary material
Funding
 References
 
Supplementary material can be found at http://carcin.oxfordjournals.org/.


   Funding
Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 Supplementary material
 Funding
References
 
Canadian Institutes of Health Research (CRT-43821) to J.M., B.B., J.K., S.G., R.G., P.P. and B.Y.; National Cancer Institute, National Institutes of Health under Request For Applications CA-95-011 (U01 CA074783 [GenBank] ); American Institute for Cancer Research (99B055) to B.B. and J.K.; Graduate studentship from the Team in Interdisciplinary Research on Colorectal Cancer with funding from the CIHR, graduate studentships from the University of Toronto (Frank Fletcher Memorial Fund and Laboratory Medicine and Pathobiology Graduate Award), Samuel Lunenfeld Research Institute to MM.

MM is a Research Student of the Canadian Cancer Society through an award from the National Cancer Institute of Canada (018668).


   Acknowledgments
 
The content of the manuscript neither does necessarily reflect the views or policies of the National Cancer Institute or any of the collaborating centers in Cancer Family Registry nor does mention of trade names, commercial products or organizations imply endorsement by the US Government or Cancer Family Registry. The authors had full responsibility for the design of the study, the collection of data, the analysis and interpretation of the data, the decision to submit the manuscript for publication and the writing of the manuscript.

Conflict of Interest Statement: None declared.


   References
Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 Supplementary material
 Funding
 References
 

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Received July 19, 2007; revised August 31, 2007; accepted September 28, 2007.


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