A systematic review of the relationship between polymorphic sites in the estrogen receptor-beta (ESR2) gene and breast cancer risk
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- Yu, K., Rao, N., Chen, A. et al. Breast Cancer Res Treat (2011) 126: 37. doi:10.1007/s10549-010-0891-2
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The estrogen signal is mediated by the estrogen receptor (ER). The specific role of ER-beta, a second ER, in breast carcinogenesis is not known. A number of association studies have been carried out to investigate the relationship between polymorphic sites in the ESR2 gene and breast cancer risk, however, the results are inconsistent. We searched PubMed, Medline, and Web of Science database (updated to 10 January 2010) and identified 13 relevant case–control studies, and approximately 28 single-nucleotide polymorphisms (SNPs) and one micro-satellite marker were reported in the literature. The median number of study subjects was 776 (range 158–13,550). Three genetic variants [(CA)n, rs2987983, and rs4986938] showed significant overall associations with breast cancer, and rs4986938 was reported twice. Because rs4986938 and rs1256049 were the most extensively studied polymorphisms, we subsequently conducted a meta-analysis to evaluate their relationship with breast cancer risk (9 studies of 10,837 cases and 16,021 controls for rs4986938; 8 studies of 11,652 cases and 15,726 controls for rs1256049). For rs4986938, the women harboring variant allele seemed to be associated with a decreased risk either in the dominant model [pooled OR = 0.944, 95% confidence interval (95% CI) 0.897–0.993, fixed-effects] or in the co-dominant model (AG vs. GG) (OR = 0.944, 95% CI 0.895–0.997, fixed-effects). rs1256049 was not associated with breast cancer risk in any model. Five studies had investigated the effect of haplotypes in the ESR2 gene on breast cancer risk, and four of them had positive outcomes. In summary, the present systematic review suggests that SNP rs4986938 as well as haplotypes in the ESR2 gene might be associated with breast cancer. The need for additional studies examining these issues seems of vital importance.
KeywordsESR2PolymorphismBreast cancerSystematic reviewMeta-analysis
Estrogen plays an important role in the development of breast cancer . The estrogen signal is mediated by the estrogen receptor (ER), which is a transcription factor belonging to the steroid hormone receptor super-family. The second ER, ER-beta, was identified in 1996 , and since then the former ER has been called ER-alpha. ER-alpha and ER-beta are coded by two separate genes, ESR1 on chromosome 6 and ESR2 on chromosome 14 . Both ER-alpha and ER-beta proteins are expressed in normal breast luminal epithelial cells as well as in breast tumors [4, 5].
Whereas the specific functions of ER-beta in breast carcinogenesis are not known yet, in vitro studies suggest that ER-beta variations may influence the susceptibility to and development of breast cancer [5, 6]. Given the potential role of ER-beta variations in breast carcinogenesis, it is reasonable to speculate that polymorphic sites in the ESR2 gene might be associated with risk of breast cancer. The ESR2 genetic variants have been investigated for their associations with body weight , menstrual disorders , anorexia nervosa , Alzheimer’s disease , and prostate cancer . With regard to breast cancer, a number of association studies have been carried out, though the results are inconsistent.
In this study, we carried out a systematic review and a meta-analysis focusing on the relationship between polymorphisms within the ESR2 gene and breast cancer risk.
Relevant studies were selected by searching PubMed, Medline, and Web of Science database (updated to 10 January 2010) using the following search terms: (ESR2 or ESR-2 or “estrogen receptor beta” or ER-beta or ER-β) and (polymorphism* or variant* or variation*) and breast. Eligible studies were retrieved and examined carefully. Their references were checked as well for other relevant publications. Review articles were also inspected to find additional eligible studies. Only studies published in English were included for systematic review and meta-analysis; we did not define any minimum number of subjects to be included. For overlapping studies, all of them were described in systematic review, but only the one with the largest sample number was included for meta-analysis.
Eligible studies and data extraction
The identified articles were assessed independently by two of the authors (K.-D. Yu and A.-X. Chen), and any discrepancy in studies’ eligibility were adjudicated by Professor Z.-M. Shao. The inclusion criteria were as following: (i) evaluation of the association between polymorphic sites in the ESR2 gene and breast cancer risk (cancer patients vs. cancer-free controls), (ii) retrospective case–control studies or prospective cohort studies, (iii) having available odds ratio (OR) with its 95% confidence interval (95% CI) of polymorphisms or haplotypes, or with sufficient available genotyping data to estimate these parameters, and (iv) fulfilling Hardy–Weinberg equilibrium (HWE). Departure from HWE or not was evaluated in the control population with the same ethnicity (P < 0.01 indicating a departure from HWE), but a deviation from HWE in a mixed control population was allowed [12, 13]. Studies should meet (i)–(iii) criteria for systematic review, and should meet all the four criteria for meta-analysis. Any study with wrong data or inconsistent data was excluded. The following variables were extracted from each study if available: first author’s surname or study organization name, publication year, source of controls (hospital-based or population-based), ethnicity, genetic variants studied, and numbers of cases and controls in different genotypes of studied polymorphisms whenever possible. Information was carefully extracted from all the eligible publications, independently by two of the authors (K.-D. Yu and A. X. Chen). Disagreement was resolved by discussion between the authors. If they could not reach a consensus, another investigator (Z. M. Shao) adjudicated over the disagreement.
Meta-analysis was mainly performed as described previously [14, 15]. Briefly, for each study, the OR with its 95% CI was calculated to assess the association strength between a certain polymorphism and breast cancer risk. The pooled OR was calculated by a fixed-effects model (using the Mantel–Haenszel method) or a random-effects model (using the DerSimonian and Laird method) according to the heterogeneity among studies. Heterogeneity assumption was checked by the Q test and a P value >0.10 indicated a lack of heterogeneity. If P < 0.10, the between-study heterogeneity was considered to be significant, and we chose the random-effects model to calculate the pooled OR; otherwise, the fixed-effects model was employed. Four different types of OR were calculated: (i) aa genotype versus AA genotype, (ii) Aa genotype versus AA genotype, (iii) aa + Aa genotypes versus AA genotype (the dominant model), and (iv) aa genotype versus Aa + AA genotypes (the recessive model). The potential publication bias was examined visually in a funnel plot of log [OR] against its standard error (SE), and the degree of asymmetry was tested using Egger’s test (P < 0.05 considered to be statistically significant). We also performed influence analysis by omitting each study to find potential outliers. All of the statistical analyses were performed using Stata/SE version 10.0 (Stata Corporation, College Station, TX, USA).
Characteristics of all the eligible studies regarding polymorphisms in the ESR2 gene and breast cancer risk
OR (95% CI)
Factors of OR adjustment
Included in the meta-analysis
Risk factors distribution in cases versus controls
Försti et al. 
nt805(del21); 846G > A; rs1256049; rs4986938; (CA)n; 1505-4 A > G
Case: post-menopausal women, mean age of 63 years (range 50–76) and did not belong to breast cancer families.
Controls: from same geographic areas and matched for ethnicity.
Zheng et al. 
rs1271572; −11943G > A; rs3829768; Int5(16-bp down of exon4); rs1256049; rs1256054; 50766A > G; 50995G > A
Adjusted for menopausal status, age, age at first birth, age at menarche, BMI, and family history
Age 47.79 ± 7.99 versus 47.24 ± 9.11 years (the whole population of Shanghai Breast Cancer Study).
Age at menarche ≤14 years: 52.84% versus 48.26%.
First degree of relatives with breast cancer: 3.7% versus 2.44%.
Age at menopause ≥52 years: 20.96% versus 16.01%.
Age at first live birth ≤27 years: 67.07% versus 71.33%.
Gold et al. a
rs1255998; rs928554; rs1152579; rs4986938; rs1256049; E2EX4CorT; rs1256030; rs1271572
Stratified by ethnicity and age
Maguire et al. a
rs1256049; rs4986938; rs928554
Stratified by family history
Of the breast cancer cases: 323 sporadic and 400 familial.
Gallicchio et al. 
rs4986938; rs928554; 5,696-bp 3′of STP-A > G; rs8018687
Adjusted for age and menopause
Iobagiu et al. 
Adjusted for three microsatellites’ combination
Age: median 60 years versus 48 years
Tsezou et al. 
Adjusted for BMI, age, age at menarche, menopause, and family history
Age: mean 57.6 years versus 70.9 years
Age of menarche: 12.75 years versus 12.89 years
Age of menopause: 47.6 years versus 48.9 years
BMI: 27.4 versus 26.2
rs1256049; rs1256031; rs3020450
Treeck et al. 
Sonestedt et al. b
rs915057; rs1269056; rs1256033; rs3020450; rs3020443
Stratified by enterolactone concentration
Age: 56.6 years (50.9-62.4) versus 56.6 years (50.8–63)
Nonsmokers: 42 versus 46%
Current hormone therapy use: 33 versus 21%
Surekha et al. 
MARIE-GENICA Consortium a
rs944050; rs4986938; rs1255998; rs1271572; rs1256049; rs928554
Adjusted for estrogen/progesterone mono-therapy, tibolone, unknown hormone, type of menopause, number of births, breastfeeding, smoking, number of mammograms, benign breast disease, family history, and BMI
With benign breast disease: 41.3 versus 34.4%
Smokers: 45.4 versus 48.8%
Ever user of oral contraceptives: 62.1 versus 63.9%.
First degree relative with breast cancer: 16.1 versus 11.7%.
Iwasaki et al. 
Adjusted for menopausal status, number of births, family history of breast cancer, smoking status, moderate physical activity in the past 5 years, and vitamin supplement use
Control matched for each case by age (within 5 years) and ethnicity.
Although many polymorphisms in the ESR2 gene had been studied, few investigators reported significant results for a single variant. In this systematic review, the associations that had been reported as significant by at least one study were discussed below. Regarding the overall risk estimate, three genetic variants had showed significant relationships with breast cancer in four studies [22–24, 26]; rs4986938 was reported twice [23, 26]. In the Breast and Prostate Cancer Cohort Consortium (BPC3) study  with the largest sample size, the investigators indicated that the A-allele carriers had a decrease in breast cancer risk (OR = 0.93, 95% CI 0.86–0.99), though the trend P value of unadjusted logistic regression did not reach significance. In another study, Surekha et al.  found that India women harboring the A allele of rs4986938 also had a reduced risk for breast cancer (OR = 0.41, 95% CI 0.16–0.95). Treeck et al.  found a significantly increased risk of breast cancer in variant carriers of SNP rs2987983 in Caucasian women (OR = 1.99, 95% CI 1.23–3.23); Tsezou et al.  revealed an association between micro-satellite (CA)n and breast cancer in Greek women (OR = 0.010, 95% CI 0.003–0.036; adjusted OR = 0.002, 95% CI 0.000–0.022). An additional study reported by Maguire et al.  implied that rs1256049 might decrease the breast cancer risk in Sweden women with a borderline significance (OR = 0.63, 95% CI 0.37–1.07).
Regarding gene–environment interaction, some investigators had reported interactions of ESR2 genetic variants with endogenous/exogenous exposure factors. Zheng et al.  found an increased breast cancer risk in rs1256054 variant allele carriers with long duration (>34 years) of menstruation (OR = 2.37, 95% CI 1.18–4.77). In a recent study by MARIE-GENICA Consortium , the investigators found that three SNPs (rs4986938, rs1271572, rs928554) could modify the relationship between postmenopausal breast cancer risk and estrogen monotherapy use. For rs4986938, its relationship with breast cancer risk could also be modified by isoflavone intake in different populations (Japanese Brazilian and non-Japanese Brazilian subjects) . However, no further studies attempting to reconfirm these complex interactions had been published yet.
We then reviewed the effects of haplotypes in the ESR2 gene on breast cancer risk. Five studies investigated this issue and four studies found significantly increased risks in carriers of some haplotypes [18, 19, 23, 25, 27]. Of note, two studies with the largest sample sizes (MARIE-GENICA Consortium study  and BPC3 study ) observed an obvious genetic contribution of haplotypes in the ESR2 gene to breast cancer.
Characteristics of studies included in meta-analysis of the two SNPs
Pooled ORs of the two SNPs in different genetic models
rs4986938 OR (95% CI)
rs1256049 OR (95% CI)
Overall (n = 9; 10,837:16,021)a
Caucasians (n = 4; 4,143:7,409)
Overall (n = 8; 11,652:15,726)a
Caucasians (n = 3; 4,046:6,116)
Codominant (Het. vs. Common Hom.)
Codominant (Rare Hom. vs. Common Hom.)
Dominant (Rare Hom. + Het. vs. Common Hom.)
Recessive (Rare Hom. vs. Het. + Common Hom.)
The present meta-analysis systematically reviewed the association between the genetic variants in the ESR2 gene and breast cancer risk. Our results indicate that one SNP, rs4986938, is likely to be a low-penetrant risk factor for developing breast cancer. Our systematic review also suggests that some haplotypes in the ESR2 gene are probably related to breast cancer.
To date, studies of association between polymorphisms in the ESR2 gene and breast cancer risk have yet been inconclusive. Few individual studies were statistically significant and no significant observation has been reported by more than two studies. In some cases, this might be due to a lack of statistical power in most studies. We in this study attempted to reach a more powerful conclusion by combining results for meta-analysis, and found that rs4986938 seemed to be a low-penetrance breast cancer susceptibility locus in the dominant model. It is biologically plausible because rs4986938 is located at 3′UTR of the ESR2 gene and this SNP could affect pre-mRNA splicing, mRNA stability and translatability . However, the meta-analysis results should to be treated with cautions. First, among nine study populations eligible for our meta-analysis, only two studies showed positive results of overall ORs (BPC3 study  and Surekha’s study ). The BPC3 study had the largest sample size, played a dominant role, and weighted 54.0% of the overall OR. When we performed influence analysis by omitting BPC3 study, the result showed that rs4986938 was not associated with breast cancer any more. Second, in ethnicity subgroup analysis, neither rs4986938 nor rs1256049 was associated with breast cancer risk in any genetic model. Although the null results might be caused by the relatively limited study number (only four studies for rs4986938 and three studies for rs1256049 in subgroup analysis specific to Caucasians) and small sample size, we could rule out the possibility that rs4986938 is actually not associated with breast cancer. Our overall positive results might be dominated by BPC3 study.
Several studies had reported the gene–environment interactions. Again, rs4986938 could influence breast cancer developing by modifying estrogen exposure  or isoflavone intake . Some other SNPs such as rs1271572 and rs928554 could also act as modifiers of the relationship between estrogen exposure and breast cancer risk . These results of subgroup analysis, however, should be treated with caution. Multiple hypothesis tests render the interpretation of positive results difficult. More studies with larger sample size should be required to elucidate those effects. Someone may argue that the effect of a single polymorphism within a gene might have a limited impact on breast cancer susceptibility, and a haplotype-based approach needs to be carried out for a more objective evaluation. Four studies (including two studies with the largest sample sizes: MARIE-GENICA Consortium study and BPC3 study [23, 27]) had observed the obvious haplotype effects on ESR2 genetic contribution to breast cancer. Regretfully, different studies constructed haplotype using different SNPs, which made previously significant results hard to replicate.
Some limitations of this systematic review should be acknowledged. First, in any systematic review, a major concern is the potential affect of publication bias. The most common case is the non-publication of negative studies, resulting in the outcome away from the null . Though we found no publication bias among the studies for meta-analysis, the positive outcome of rs4986938 still needs further validation. Second, there is no consensus nomenclature for all the studied genetic polymorphisms: early reports often described the restriction enzyme site involved; recent studies usually identified the base substitution. But it could also be arbitrary, since some studies presented polymorphism’s name according to its position in DNA sequence, while some presented it according to RNA or protein position. The requirement for public databases of SNPs has been recognized, and the standardized description of a SNP is to use a reference number. Third, the current overall OR is based on individual unadjusted ORs; a more precise evaluation should be adjusted by other potentially suspected factors including age, menopausal status, estrogen exposure, and environmental factors. Lastly, though most controls were selected from healthy populations, some controls were derived from women with benign breast diseases , which might lead to misclassification bias because those women have potential risks of developing breast cancer .
Despite these concerns, we believe that some conclusions could be drawn according to current evidence. First, rs4986938 is likely to be related to breast cancer risk, and it might also act as a modifier of the relationship between breast cancer risk and some environmental factors. We encourage further evaluations on the contribution of rs4986938 to breast cancer risk in larger, more comprehensive and well-designed association studies. Second, haplotypes of the ESR2 gene is implied to be associated with breast cancer. Further work is clearly needed to address these issues.
This research is supported by grants from the National Basic Research Program of China (2006CB910501), 2009 Youth Foundation of Shanghai Public Health Bureau, 2009 Youth Foundation of Shanghai Medical College, and the National Natural Science Foundation of China (30971143, 30972936).
Conflict of interest statement
All authors declared no potential conflicts of interest.