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browska91 Division of Cancer Epidemiology and Genetics, National Cancer Institute, NIH, Department of Health and Human Services, Rockville, Maryland; 2 Yale University School of Medicine, New Haven, Connecticut; 3 Cancer Prevention Research Group, Fred Hutchinson Cancer Research Center, Seattle, Washington; 4 Comprehensive Cancer Center and Department of Population Health Sciences, University of Wisconsin, Madison, Wisconsin; 5 Vanderbilt University Medical Center, Nashville, Tennessee; 6 Dartmouth Medical School, Norris Cotton Cancer Center, Lebanon, New Hampshire; 7 Core Genotyping Facility, Division of Cancer Epidemiology and Genetics, National Cancer Institute, NIH, Department of Health and Human Services, Gaithersburg, Maryland; 8 Department of Cancer Epidemiology and Prevention, M. Sklodowska-Curie Institute of Oncology and Cancer Center, Warsaw, Poland; and 9 Nofer Institute of Occupational Medicine, Lodz, Poland
Requests for reprints: Yawei Zhang, School of Epidemiology and Public Health, Yale University, 60 College Street, LEPH 440, New Haven, CT 06520. Phone: 203-785-6210; Fax: 203-737-6023. E-mail: yawei.zhang{at}yale.edu or Montserrat García-Closas, Hormonal and Reproductive Epidemiology Branch, Division of Cancer Epidemiology and Genetics, National Cancer Institute, NIH, Room 7076, 6120 Executive Boulevard, MSC 7234, Rockville, MD 20852-7234. Phone: 301-435-3981; Fax: 301-402-0916. E-mail: montse{at}nih.gov
| Abstract |
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| Introduction |
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BER includes many proteins and the genes encoding them have numerous genetic variants. XRCC1 acts as a central scaffolding protein by binding DNA ligase III, DNA polymerase ß, and poly(ADP-ribose) polymerase in BER (5-8). Two common genetic polymorphisms in XRCC1 (Q399R and R194W) have been evaluated in relation to breast cancer risk in several previous studies (9-20). The results, however, have been inconsistent. It has also been suggested that the relationship between XRCC1 Q399R and R194W and breast cancer risk might be modified by ethnicity or by family history (9-19). Polymorphisms of other genes in the BER pathway and breast cancer risk have been less explored. For this project, we analyzed eight SNPs in six BER genes (XRCC1, ADPRT, APEX1, OGG1, LIG3, and MUTYH) in one of the largest population-based case-control studies of breast cancer conducted to date, which includes 3,368 cases and 2,880 controls in the United States. We also evaluated polymorphisms in XRCC1 Q399R in a case-control study of 1,995 cases and 2,296 controls in Poland.
| Materials and Methods |
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Approximately 80% of eligible breast cancer cases and 75% of eligible controls completed the interview. Respective participation rates for buccal cell collection in cases and controls who completed the interview were 73% and 64% for cytobrush samples and 71% and 61% for mouthwash samples. Because of insufficient DNA quantity or quality, 596 of 2,097 cases and 588 of 1,993 controls with a cytobrush sample and 22 of 1,986 cases and 14 of 1,573 controls with a mouthwash sample were excluded from genotype analyses. To limit heterogeneity, analyses were further restricted to Caucasian women, mostly of central European ancestry, resulting in a total of 1,470 cases (1,311 invasive and 159 in situ) and 1,366 controls with cytobrush DNA and 1,898 cases (1,661 invasive and 237 in situ) and 1,514 controls with mouthwash DNA samples included in the analyses.
The Polish Breast Cancer Study. Eligible cases were women 20 to 74 years of age, residents of Warsaw and Lodz in Poland, and newly diagnosed with either histologically or cytologically confirmed in situ or invasive breast cancer between January 2000 and January 2003. Cases were recruited through a rapid identification system organized at participating hospitals. The Cancer Registry in Warsaw was used to identify the eligible cases missed by the rapid case identification system in each hospital. The Polish Electronic System, a database with demographic information from all residents of Poland, was used to randomly select controls stratified by city and age in 5 year categories on a quarterly basis from January 2000 to September 2003. Women provided a personal interview on known and suspected risk factors. Venous blood samples were collected by a trained nurse and DNA was isolated from buffy coat or whole blood samples. The study protocol was reviewed and approved by local and NCI IRBs. All participants provided written informed consent. Of the 3,037 eligible cases and 3,639 controls, 2,386 (79%) cases and 2,502 (69%) controls agreed to participate in the personal interview. The present study is limited to women with DNA isolated from blood samples: 1,995 (84%) cases and 2,296 (94%) controls.
Genotyping
We selected eight SNPs in six BER genes with assays available at the time of analysis at the Core Genotyping Facility of the Division of Cancer Epidemiology and Genetics, NCI. We chose SNPs that have been previously examined in relation to breast cancer [XRCC1 Q399R (rs25487; refs. 9-20), R280H (rs25489; ref. 13), R194W (rs1799782; refs. 9-12, 14, 17-20), and OGG1 S326C (rs1052133; ref. 22)] or had possible functional significance, such as missense variants [ADPRT V726W (rs1136410), APEX1 D148E (rs3136820), LIG3 R780H (rs3136025)] or variants in regulatory sequences [MUTYH 5' untranslated region (5'UTR), rs3219466]. DNA was extracted from mouthwash samples collected in the U.S. breast cancer study and was genotyped for the eight SNPs at the Core Genotyping Facility of NCI. DNA extracted from cytobrush samples collected in the U.S. study and blood DNA samples from the Polish study were genotyped for XRCC1 Q399R (rs25487). Description and methods for each genotype assay can be found at http://snp500cancer.nci.nih.gov (23). Duplicated DNA samples were included for quality control (150 cytobrush DNA and 187 mouthwash DNA in the U.S. study and 100 blood DNA in the Polish study). All assays had
99% concordance rates, except for XRCC1 R280H (98%), in the U.S. study. We observed no significant departures from Hardy-Weinberg equilibrium in the U.S. Caucasian or Polish control populations for any of the SNPs analyzed (Table 1). Three different types of DNA sources (mouthwash, cytobrush, and blood) were used for genotyping XRCC1 Q399R. The minor allele frequencies among controls were very similar for different DNA sources (35.3% in mouthwash, 37.8% in cytobrush, and 36.2% in blood).
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Meta-analyses. Meta-analyses were done to summarize our findings along with those of published studies of the association between breast cancer risk and two polymorphisms in XRCC1 (Q399R and R194W). Peer-reviewed studies published in June 2005 in English on the relationship between XRCC1 and breast cancer risk were located using PubMed. Crude ORs and 95% CIs were calculated for all studies using published frequencies for cases and controls by the genotype of interest. Analyses were conducted overall and separately in Caucasian and Asian women. A random-effect model (24) in STATA (Version 8.2, Special Edition) was employed to estimate summary ORs and 95% CIs by weighing each study result by a factor of within- and between-study variance. Homogeneity of study results in different groups was assessed by the Q test and publication bias by Begg's test (25) and Egger's test (26).
| Results |
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Further analyses in the U.S. breast cancer study stratified by family history of breast cancer in first-degree relatives did not modify the associations between SNPs in XRCC1, ADPRT, APEX1, OGG1, LIG3, and MUTYH genes and breast cancer risk (data not shown). Findings were also similar for in situ and invasive breast cancer (data not shown). Pairwise D' values, estimated using HaploView (27), indicated that the three XRCC1 SNPs are in strong linkage disequilibrium in the U.S. breast cancer study (D' > 0.96) although the correlation between SNPs was low (r2 < 0.05).
Meta-analyses. Results from meta-analyses of two polymorphisms (Q399R and R194W) in the XRCC1 gene are presented in Table 3. The meta-analyses summarize the data presented here from the U.S. and Polish studies, data from 12 studies (9-20) that investigated the relationship between Q399R and breast cancer risk and 9 studies (9-12, 14, 17-20) that investigated the relationship with XRCC1 R194W. Summary estimates showed no significant associations between these two SNPs and breast cancer risk in all women (total of 10,934 cases and 11,543 controls for Q399R and total of 5,752 cases and 6,050 controls for R194W) or in separate analyses of Caucasian women (total of 7,824 cases and 8,226 controls for Q399R and total of 3,822 cases and 4,015 controls for R194W). However, in Asian women (total of 1,567 cases and 1,643 controls), we noted a significant 60% increased risk for women who carried homozygous A genotype compared with women who carried homozygous G genotype of XRCC1 Q399R (95% CI, 1.1-2.3). We found no significant study heterogeneity according to the Q test or publication bias according to Begg's or Egger's tests for either overall populations or different ethnic groups (data not shown).
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| Discussion |
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Epidemiologic studies of XRCC1 Q399R and breast cancer risk have provided some evidence of increased risk associated with the A allele among African Americans (9) and Asians (10, 18). Studies among Caucasians, however, have consistently found no association (11-17, 19). The lack of association in Caucasian populations was confirmed by both the U.S. and Polish breast cancer studies in this report. Summary estimates from our meta-analysis (total of 7,824 cases and 8,226 controls) showed no evidence of an association between XRCC1 Q399R and breast cancer risk in Caucasian populations [OR, 1.0 (95% CI, 0.9-1.1), for homozygous variants versus wild-type]. However, when the meta-analysis was restricted to four studies of Asian populations (total of 1,567 cases and 1,643 controls), there was a significant 60% increased risk for XRCC1 Q399R homozygous variants versus wild-type (OR, 1.6; 95% CI, 1.1-2.4). Only one study including 253 cases and 266 controls evaluated the association between XRCC1 Q399R and breast cancer risk among African Americans, noting an 70% increased risk associated with heterozygous or homozygous A genotype (OR, 1.7; 95% CI, 1.1-2.4; ref. 9). The frequency of the variant A allele was significantly different among the three ethnic groups (Caucasian, 36%; Asian, 30%; African, 14%; P = 0.0006), which was very similar with the number from a recently published meta-analysis of XRCC1 polymorphisms and cancer risk (28). Summary estimates for XRCC1 Q399R homozygous variants versus wild-type and overall cancer risk presented in that meta-analysis (28) are consistent with an increased risk in Asian (OR, 1.16; 95% CI, 0.98-1.38) or African (OR, 1.43; 95% CI, 0.68-2.99) populations, but not in European populations (OR, 0.96; 95% CI, 0378-1.19). However, it is unclear that the observed differences by race have a biological basis and genetic effects for complex diseases tend to be consistent across human populations (29). Therefore, further evidence is needed to make a conclusion about potential differences in relative risk by race.
Studies of XRCC1 R194W and breast cancer risk have been inconsistent, with some suggesting an increased risk (11, 18), a reduced risk (9, 14, 17), or no association (10, 13, 19). We found no association in the U.S. women, and summary estimates from our meta-analysis provided no evidence of an association either among all populations [OR, 1.0 (95% CI, 0.8-1.2), based on 5,752 cases and 6,050 controls] or Caucasians [OR, 0.9 (95% CI, 0.8-1.1), based on 3,822 cases and 4,015 controls]; this result was also supported by a previous meta-analysis (28).
Very few studies have investigated associations between other genetic variants in BER pathway and breast cancer risk. One study in Asians (123 cases and 123 controls) found no association between XRCC1 R280H and breast cancer risk (18). One study among Caucasians (254 cases and 312 controls) reported an 80% increased risk associated with the XRCC1 R280H homozygous or heterozygous A genotype (13). However, this increased risk was not confirmed in the present study of U.S. women. We also found no association between OGG1 S326C and breast cancer risk, consistent with a previous study of 434 cases and 434 controls (22).
A strength of our investigation is the availability of two large population-based studies in Caucasian populations with good participation rates. The mouthwash component of the U.S. study that was used to screen for potentially interesting findings had sufficient power to detect small to moderate associations between the genetic polymorphisms evaluated and risk of breast cancer. Additional samples from women with cytobrush DNA in the U.S. study allowed a substantial increase in sample size to assess potential associations, and the Polish study served as an independent replication study. The analytic strategy also minimized the probability of reporting false-positive findings. Finally, compared with a recently published meta-analysis (28), our meta-analyses had substantially larger number of breast cancer cases (2,382 in Hu et al.'s study versus 10,934 in ours for Q399R and 2,476 versus 5,752 for R194W) and controls (2,780 versus 11,543 for Q399R and 2,122 versus 6,050 for R194W). The meta-analyses for associations evaluated in previous studies permitted a more definite conclusion about these associations. Although this is a large study, the power to detect associations with rare SNPs (i.e., XRCC1 R280H, XRCC1 R194W, LIG3 R780H, and MUTYH 5'UTR) was limited, resulting in relatively wide confidence intervals. We used an approach that preferentially selected coding SNPs in candidate genes and did not perform a dense survey of SNPs intended to characterize haplotype diversity. Therefore, it is possible that common genetic variation in the BER genes not captured by our approach could be related to breast cancer risk. Other alternative approaches, such as selecting haplotype tagging SNPs, should be considered.
In summary, we provide evidence against a substantial association between XRCC1 Q399R and R194W and breast cancer risk, with the possible exception of an association for Q399R in Asian populations. The U.S. breast cancer study also showed no evidence for an association with SNPs evaluated in other BER genes and the results were not changed after stratified by menopausal status and family history. These findings indicate that the genetic variants in six BER genes evaluated in this report are unlikely to play a major role on breast carcinogenesis, particularly in Caucasian populations.
| 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.
Received 8/23/05; revised 10/31/05; accepted 12/ 5/05.
| References |
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