Association between androgen receptor gene CAG repeat polymorphism and breast cancer risk: a meta-analysis

Androgens have been hypothesized to influence risk of breast cancer through several possible mechanisms, including their conversion to estradiol and their binding to the estrogen receptor and/or androgen receptor (AR) in the breast. The CAG repeat polymorphism in AR exon 1 has been implicated in breast cancer risk; however, studies on the association between this polymorphism and breast cancer risk remain conflicting. In order to derive a more precise estimation of the relationship, a large population-based case–control study was performed. We found that a long CAG sequence has a protective effect on breast cancer using an a priori determined cutoff (<22 or ≥22) in a dominant model analysis [SL–LL vs. SS, odds ratio (OR) = 0.86, 95% confidence intervals (CI): 0.67–1.10]. A similar result was obtained by analyzing seven detailed genotyping case–control studies by allele comparison in dominant and recessive models. However, larger scale primary study is required to further evaluate the interaction of AR CAG polymorphism and breast cancer risk.     

Association of the progesterone receptor gene with endometrial cancer risk in a Chinese population

BACKGROUND:

Single nucleotide polymorphisms (SNPs) in the progesterone receptor (PGR) gene have been associated with the risk of endometrial cancer. However, to the authors' knowledge, no study to date has systematically evaluated the role of the PGR gene in endometrial carcinogenesis.

METHODS:

Exposure information and DNA samples collected in the Shanghai Endometrial Cancer Study, a population‐based case‐control study of 1204 incident cases and 1212 age‐ and frequency‐matched population controls, were used in this study. Seven tag SNPs were identified for the PGR gene plus the 5‐kilobase (kb) flanking regions using the Han Chinese data from the HapMap project with a pairwise correlation coefficient (r²) ≥ 0.90. These 7 SNPs captured 92% of SNPs in the region with a pairwise r² ≥ 0.90 or 100% of SNPs with a pairwise r² ≥ 0.80. Genotyping of polymorphisms was performed by using the Affymetrix MegAllele Targeted Genotyping System. A logistic regression model was used to compute adjusted odds ratios (ORs) and 95% confidence intervals (95% CIs).

RESULTS:

Of 7 tag SNPs that were assessed, 2 polymorphisms in the 3′ flanking region of the PGR gene, reference SNP identification number (rs) 11224561 (rs11224561) and rs471767, were associated with the risk of endometrial cancer. The cytosine/cytosine (CC) genotype of SNP rs11224561 was associated with decreased risk (OR, 0.68; 95% CI, 0.50‐0.92) compared with the thymine/thymine (TT) genotype. Carrying the guanine (G) allele of the rs471767 SNP also was associated with decreased risk, although the association was not statistically significant (OR, 0.78, 95%CI, 0.59‐1.04 and OR, 0.32, 95%CI, 0.03‐3.05 for the adenine [A]G and GG genotypes, respectively, compared with the homozygote AA).

CONCLUSIONS:

The current findings suggested that polymorphisms in the 3′ flanking region of the PGR gene may be associated with the risk of endometrial cancer. Cancer 2009. © 2009 American Cancer Society.     

A functional polymorphism in the progesterone receptor gene is associated with an increase in breast cancer risk

Biological and epidemiological data suggest that progesterone has an important role in mammary tumorigenesis. Because the effects of progesterone require the progesterone receptor (PGR), which exists in two isoforms, PR-A and PR-B, we sought to determine whether the functional polymorphism, +331 G/A, which causes an increase in the expression of the hPR-B isoform, is related to breast cancer risk. Using a nested case-control study design within the Nurses' Health Study cohort, we genotyped 990 cases and 1,364 controls and observed a statistically significant increased risk of breast cancer among carriers of the +331 A allele (odds ratio, 1.33; 95% confidence interval, 1.01-1.74) compared with subjects with the GG genotype. We also observed a potential interaction between genotype and body mass index (BMI) among postmenopausal women, with the highest risk (odds ratio, 2.30; 95% confidence interval, 1.02-5.21) among obese women (BMI >/=30 kg/m(2)) with the GA or AA genotype compared with lean (BMI <25 kg/m(2)) women with the GG genotype. Our findings suggest that the increased production of hPR-B by the +331 G/A polymorphism may predispose women to breast cancer development through increased hPR-B-dependent stimulation of mammary cell growth.     

Association of progesterone receptor gene polymorphism (PROGINS) with endometriosis, uterine fibroids and breast cancer

Endometriosis, uterine fibroids and breast cancer are female health disorders associated with a great deal of morbidity. Since all these disorders are hormone responsive, our present study has been carried out to identify the association of 306bp Alu insertion polymorphism in intron 7 of progesterone receptor gene (PROGINS). DNA was isolated from the blood samples of 445 Asian Indian women, which included 100 endometriosis, 80 fibroids and 157 cases of breast cancer along with 108 age matched normal healthy women as controls. PROGINS polymorphism was assessed by PCR followed by agarose gel electrophoresis. Results showed that T2 allele frequency is 5%, 10% and 14.6% in endometriosis, uterine fibroids and breast cancer, as compared to 5.5% in controls. This indicates that PROGINS can be considered as a predisposing risk marker for breast cancer but not for endometriosis and uterine fibroids.     

Association of progesterone receptor gene (PGR) variants and breast cancer risk in African American women

Prolonged exposure to combined hormone replacement therapy (estrogen plus progestin) increases a woman’s risk of breast cancer, whereas estrogen-only hormone replacement therapy does not. This suggests that progesterone may play a role in breast carcinogenesis. Association studies have reported inconsistent relationships between progesterone receptor gene variants and breast cancer. A population-based case–control study in three counties of the Philadelphia Metropolitan area was undertaken. We evaluated 8 PGR candidate SNPs and 18 PGR tagging SNPS in 487 breast cancer cases and 843 controls using multivariable logistic regression with adjustment for combined hormone replacement therapy use. Separate analyses were conducted for European Americans (EA: 399 cases, 490 controls) and African Americans (AA: 88 cases, 353 controls). In EAs, no significant associations were observed with the investigated PGR variants. In AAs, two tagging SNPs (rs590688 and rs10895054) were statistically significantly associated with breast cancer. For rs590688, each addition of the C allele was protective compared to the G allele (OR = 0.56, 95 % CI 0.39–0.82, p value 0.003, corrected p value 0.03). For rs10895054, each addition of the T allele increased the risk of breast cancer compared to the A allele nearly threefold (OR = 2.9, 95 % CI 1.47–6.02, p value 0.002, corrected p value 0.04). Three haplotype blocks, all containing rs590688, were found to be significantly associated with breast cancer risk. Environmental exposures, namely parity and obesity modified the effect of both SNPs on breast cancer risk in EA. This is the first study to find an association between two PGR variants and breast cancer in AA women. These results suggest that studies of PGR variants in other non-White populations may reveal additional cancer associations of interest.     

Association of breast cancer progression with a vitamin D receptor gene polymorphism. South-East Sweden Breast Cancer Group.

The vitamin D3 receptor gene (VDR) contains a TaqI RFLP that is associated with increased VDR mRNA stability, increased serum levels of 1alpha,25-dihydroxyvitamin D3 (1,25-D3), and decreased risk for prostate cancer. Determination of the TaqI genotype, in a group of young women with breast cancer (n = 111; age, <37 years) and a control population (n = 130), revealed no overall association to risk for breast cancer. However, patients without TaqI site (TT genotype) showed a significantly increased risk for lymph node metastasis (relative risk, 1.8, 95% confidence interval, 1.3-2.6). Furthermore, a tendency toward an increased survival was found among estrogen receptor-positive, tamoxifen-treated patients who were homozygous for the TaqI site (P = 0.075). We conclude that polymorphism in the VDR gene may influence tumor progression and tamoxifen treatment response in early-onset breast carcinomas.     

Association of the CYP17 gene polymorphism with the risk of prostate cancer: a meta-analysis.

A T-to-C polymorphism in the 5' promoter region of the CYP17 gene that encodes the cytochrome P450c17alpha has been implicated as a risk factor for prostate cancer, but individual studies have been inconclusive or controversial. Therefore we performed a meta-analysis of 10 studies (12 comparisons) with CYP17 genotyping on 2404 patients with prostate cancer and 2755 controls. Overall, the random effects odds ratio (OR) for the A2 (C) versus A1 (T) allele was 1.08 [95% confidence interval (CI), 0.95-1.22], with some between-study heterogeneity (P = 0.04). There was no suggestion of an overall effect either in recessive or dominant modeling of A2 effects, and the comparison of A2/A2 versus A1/A1 also showed no differential susceptibility to prostate cancer (OR, 1.15; 95% CI, 0.91-1.46). No effect of A2 was seen in subjects of European descent (7 comparisons, OR, 1.04; 95% CI, 0.92-1.18, no significant between-study heterogeneity) or Asian descent (2 comparisons, OR, 1.06; 95% CI, 0.66-1.71; P = 0.02 for heterogeneity), whereas A2 increased susceptibility to prostate cancer in subjects of African descent (3 comparisons, OR, 1.56; 95% CI, 1.07-2.28; no between-study heterogeneity). Smaller studies unilaterally showed more prominent genetic effects for A2 than larger studies (P = 0.038). The meta-analysis suggests that the CYP17 polymorphism is unlikely to increase considerably the risk of sporadic prostate cancer on a wide population basis, especially in subjects of European descent. Previously reported associations may reflect publication bias, although it is also possible that the polymorphism may be important in subjects of African descent.     

Association of vitamin D receptor gene polymorphism with sporadic breast cancer in Taiwanese patients

BRCA1 protein is normally expressed in the nuclei of breast epithelial cells and functions as a negative regulator of the cell cycle. Mutations of BRCA1 gene have been associated with familial breast carcinomas. Although somatic mutations have not been demonstrated in sporadic breast carcinomas, loss of nuclear expression of BRCA1 protein has been correlated with high-grade, infiltrating breast carcinomas in females. We have investigated the expression of BRCA1 protein in a series of 26 infiltrating carcinomas of male breast and correlated the results with a variety of clinicopathological parameters. Immunohistochemical analysis demonstrated decreased expression of BRCA1 in all carcinomas compared to normal breast epithelium. The median survival was 8 years in patients with minimal loss of BRCA1 expression while it was 1.5 years in patients with marked loss of this protein. Marked loss of BRCA1 protein was also associated with increased cell proliferation. These results suggest that BRCA1 plays a similar role in both male and female breast carcinoma and loss of this protein is associated with poor prognosis.     

Association between CYP17 gene polymorphism and risk of breast cancer in young women.

Long-term exposure to oestrogens is a well-recognised risk factor for breast cancer, whereas little is known about the influence of polymorphisms of genes involved in oestrogen biosynthesis and metabolism. A candidate, containing a single bp polymorphism, T-->C, (designated, A2 allele), might be the CYP17 gene, which codes for an enzyme involved in oestrogen synthesis. This polymorphism creates an additional Sp1-type promoter site (CCACC box), which has been shown to be associated with increased serum oestrogen levels. We performed a case-control study, to evaluate association of the CYP17 gene polymorphism with risk of breast cancer in young women (younger than 37 years). We found a statistically significant increased risk in carriers of at least 1 A2 allele [odds ratio (OR), 2.0; 95% confidence interval (CI), 1.1-3.5, p = 0.027], and a trend toward a gene-dose effect illustrated by a slightly higher risk for A2-homozygous subjects (OR, 2.8) than for heterozygous women (OR, 1. 9). Furthermore, when we investigated the CYP17 genotype in relation to tumour characteristics, breast cancer patients with 1 or 2 A2 alleles tended to have lower oestrogen receptor levels (risk ratio, 0.70; CI, 0.41-1.2, p = 0.44). Our findings suggest that CYP17 gene polymorphism influences breast carcinogenesis in young women. Int. J. Cancer (Pred. Oncol.) 84:350-353, 1999.     

Association of a vascular endothelial growth factor gene 936 C/T polymorphism with breast cancer risk: a meta-analysis

Published studies on the association between the vascular endothelial growth factor (VEGF) gene 936 C/T polymorphism and breast cancer risk are inconclusive, and a meta-analysis is required to verify the association. Nine studies, including a total of 4,973 cases and 5,035 controls, were subjected to meta-analysis. When all eligible subjects were pooled for meta-analysis, the CT + TT genotypes were not associated with a significant decrease in breast cancer risk (odds ratio = 0.87; 95% confidence interval 0.75–1.02; P = 0.087). We also categorized by ethnicity (Caucasian, Asian, or mixed) for subgroup analysis, however, according to this subgroup analysis, we found no significant association between the CT and TT versus CC genotype with breast cancer risk reduction in any of the subgroups. We conclude that the VEGF gene 936 C/T polymorphism does not affect breast cancer risk.     

Association between vitamin D receptor poly(A) polymorphism and breast cancer risk: a meta-analysis

Vitamin D receptor (VDR) poly(A) is a common genetic polymorphism in the VDR gene, and it has been implicated to be associated with breast cancer risk. However, previous studies on the association reported inconclusive results. We performed this meta-analysis to comprehensively assess the association. Eligible studies were searched in PubMed and EMBASE databases. Odds ratio (OR) and its 95 % confidence interval (95 % CI) were used for statistical analysis. A total 6,631 cases and 6,718 controls from 11 case–control studies were finally included into the meta-analysis. Meta-analysis of total eligible studies showed that VDR poly(A) polymorphism was not associated with the risk of breast cancer (S versus L: OR?=?0.99, 95 % CI of 0.90–1.09, P?=?0.84; SS versus LL: OR?=?0.96, 95 % CI of 0.79–1.18, P?=?0.70; SS/LS versus LL: OR?=?0.96, 95 % CI of 0.83–1.12, P?=?0.63; SS versus LL/LS: OR?=?1.00, 95 % CI of 0.91–1.10, P?=?0.98). Meta-analysis of studies with high quality also showed that there was no association between VDR poly(A) polymorphism and breast cancer risk. In addition, in the subgroup analysis by ethnicity, no significant association was found among Caucasians. Therefore, the meta-analysis suggests that VDR poly(A) polymorphism is not associated with the risk of breast cancer. Large well-designed studies are necessary to clarify the possible association in Asians.     

Association between vitamin D receptor gene Cdx2 polymorphism and breast cancer susceptibility

Vitamin D receptor (VDR) gene polymorphisms have been reported to influence susceptibility to breast cancer. However, published findings on the association between VDR Cdx2 polymorphism and breast cancer susceptibility are conflicting. To get a precise estimation of the association between VDR Cdx2 polymorphism and breast cancer susceptibility, we conducted a meta-analysis of four case–control studies with a total of 8,880 subjects (3,841 cases and 5,039 controls). The results showed that VDR Cdx2 polymorphism was not associated with risk of breast cancer (A versus G: OR?=?0.96, 95 % CI 0.84–1.09; AA versus GG: OR?=?0.97, 95 % CI 0.64–1.45; AA/GA versus GG: OR?=?0.94, 95 % CI 0.80–1.10; AA versus GG/GA: OR?=?0.99, 95 % CI 0.65–1.51). Subgroup analysis in Caucasians also showed that VDR Cdx2 polymorphism was not associated with risk of breast cancer in Caucasians. However, there was a significant association in Africans (A versus G: OR?=?0.75, 95 % CI 0.60–0.94; AA versus GG: OR?=?0.53, 95 % CI 0.29–0.99; AA/GA versus GG: OR?=?0.75, 95 % CI 0.57–0.97). Therefore, the association between VDR Cdx2 polymorphism and breast cancer susceptibility is only found in Africans. More studies are needed to further assess the association in Asians or Africans.     

Progesterone receptor gene polymorphism is associated with decreased risk for breast cancer by age 50

In a population-based case-control study for breast cancer before the age of 51 years, 554 cases and 559 age-matched controls were genotyped for the polymorphic progesterone receptor allele PROGINS. Breast cancer risk was decreased in women carrying the PROGINS allele. The odds ratio adjusted for age and study region was 0.76 [95% confidence interval (CI), 0.58-1.00]. Compared with wild-type A1/A1 homozygotes, the odds ratio for A1/A2 heterozygotes and A2/A2 homozygotes was 0.82 (95% CI, 0.62-1.08) and 0.27 (95% CI, 0.10-0.74), respectively, suggesting a gene dosage effect of the A2 allele. There was suggestive evidence for a differential effect by menopausal status (P = 0.07) and by family history of breast cancer (P = 0.15).     

Association of breast cancer risk with a common functional polymorphism (Asp327Asn) in the sex hormone-binding globulin gene.

Sex hormones play a central role in the development of breast cancer. Sex hormone-binding globulin (SHBG) modulates the bioavailability of circulating sex hormones and regulates their signaling system in the breast tissue. We evaluated the association of a common functional polymorphism (Asp327Asn) in the SHBG gene with breast cancer risk in a population-based case-control study (1,106 cases and 1,180 controls) conducted in Shanghai, China. The variant Asn allele was associated with a reduced breast cancer risk in postmenopausal women [odds ratio (OR), 0.73; 95% confidence interval (95% CI), 0.53-0.99], but not in premenopausal women (OR, 1.03; 95% CI, 0.82-1.27). The protective association was much stronger in postmenopausal women with a low body mass index (BMI; OR, 0.46; 95% CI, 0.29-0.75) or waist-to-hip ratio (OR, 0.51; 95% CI, 0.32-0.83) than those with a high BMI or waist-to-hip ratio (P for interaction < 0.05). Furthermore, the association was stronger for estrogen receptor-positive (OR, 0.64; 95% CI, 0.42-0.98) than for estrogen receptor-negative breast cancer (OR, 0.85; 95% CI, 0.50-1.45). Among postmenopausal controls, blood SHBG levels were 10% higher in carriers of the variant Asn allele than noncarriers (P = 0.06). Postmenopausal control women with the Asn allele and low BMI or waist-to-hip ratio had 20% higher SHBG levels (P < 0.05). This study suggests that the Asn allele in the SHBG gene may be related to a reduced risk of breast cancer among postmenopausal women by increasing their blood SHBG levels.