The androgen receptor CAG repeat polymorphism and risk of breast cancer in the Nurses' Health Study

Shorter alleles of a polymorphic [CAG](n) repeat in exon 1 of the androgen receptor (AR) have been associated with increased risk of prostate cancer and decreased risk of breast cancer. We prospectively assessed the association between the [CAG](n) repeat polymorphism in the androgen receptor and breast cancer risk among Caucasian women in a case-control study nested within the Nurses' Health Study cohort (cases, n = 727; controls, n = 969). In addition, we assessed whether androgen receptor genotype influences endogenous steroid hormone levels in women and whether the associations between androgen receptor alleles and breast cancer risk differed according to established breast cancer risk factors. Women with one or more long AR [CAG](n) repeat alleles (>or=22 repeats) were not at increased risk of breast cancer [odds ratio (OR), 1.06; 95% confidence interval (CI), 0.83-1.35]. Significant associations were not observed between AR genotypes comprised of two short alleles ([CAG](n) or=22: OR, 0.92; 95% CI, 0.62-1.36) or two long alleles ([CAG](n) >or= 25 versus both alleles or=22; OR, 1.70; 95% CI, 1.20-2.40; P for interaction = 0.04). In summary, we observed no overall relation of AR genotype with breast cancer risk among mostly postmenopausal Caucasian women. However, these data suggest that longer AR [CAG](n) repeat alleles may increase breast cancer risk among women with a first-degree family history of breast cancer.     

Esophageal cancer risk in relation to GGC and CAG trinucleotide repeat lengths in the androgen receptor gene

The incidence of esophageal squamous cell cancer in African males in South Africa is one of the highest in the world. Because most patients present with advanced disease such that survival is poor, the identification of high-risk individuals will facilitate early disease detection. Two polymorphic triplet repeats-(CAG)(n) and (GGC)(n)-in the androgen receptor gene were evaluated as potential genetic susceptibility loci for esophageal squamous cell cancer. Shorter lengths of these alleles have been reported to be associated with increased risk for prostate cancer. Our study sample comprised African males (29 patients and 109 controls), African females (14 patients and 59 controls) and Colored males (15 patients and 58 controls) whose alleles were analyzed singly and in combination. As in prostate cancer, the short (GGC)(n) alleles were implicated in esophageal cancer in African males: the average allele length was significantly shorter in patients compared to controls (p = 0.018), and a short (GGC)(n) allele was associated with elevated risk for disease [(GGC)(21) (GGC)(16)] OR 0.26, 95% CI 0.11-0.65. Analysis using logistic regression led to narrower CIs for the ORs and enabled presentation of a risk profile.     

Androgen receptor gene polymorphism and breast cancer susceptibility in The Philippines.

Up to one-third of women with breast cancer have a family history of breast cancer, and approximately 5% of cases are attributed to mutations in high-risk breast cancer susceptibility genes, such as BRCA1 and BRCA2. It is believed that genes of lower penetrance, but of greater prevalence, may also modulate a woman's risk of breast cancer. We studied the association of breast cancer and the trinucleotide repeat polymorphism (CAGn) in exon 1 of the androgen receptor gene (AR) in 299 cases of breast cancer and in 229 hospital-based controls from The Philippines. Women for whom the mean length of the CAG repeat allele was < or = 25 units had approximately one-half of the risk of breast cancer compared with women with a mean repeat length of > or = 26 [odds ratio (OR), 0.47; 95% confidence interval (CI), 0.28-0.8). The association with breast cancer risk was particularly strong among older women (> or = 50 years; OR, 0.2; 95% CI, 0.04-0.94). The association was also observed for the longer of the two AR alleles; there was a 5% increase in breast cancer risk for each unit increase in CAG repeat number. These findings support the theory that short trinucleotide repeat genotypes of the AR gene protect against breast cancer.     

Associations between ERalpha, ERbeta, and AR genotypes and colon and rectal cancer.

Estrogen and androgens are thought to be involved in the etiology of colorectal cancer. We evaluate genetic variants of the estrogen receptor genes (ERalpha and ERbeta) and the androgen receptor gene (AR). We use data from two large case-control studies of colon (n = 1,580 cases and 1,968 controls) and rectal (n = 797 cases and 1,016 controls) cancer. We evaluated the 351A >G XbaI polymorphism of ERalpha, the 1,082 G >A and CA repeat polymorphisms of ERbeta, and the CAG repeat of AR. Having two 25 or more CA repeats in ERbeta was associated with an increased relative risk of colon cancer in women [odds ratio (OR), 2.13; 95% confidence interval (95% CI), 1.24-3.64] but not in men (P(interaction) relative excess risk from interaction < 0.01; multiplicative = 0.03). Increasing number of AR CAG repeats was directly associated with colon cancer among men (OR, 1.28; 95% CI, 1.06-1.54), but not women (OR, 0.83; 95% CI, 0.68-1.02); the interaction P value for AR gene x sex was <0.01. Taking hormone replacement therapy (HRT) was associated with a reduced risk of colon cancer in the presence of the R allele of the ERbeta gene, whereas an R allele was associated with increased risk among postmenopausal women who did not take HRT. Postmenopausal women not using HRT who had > or =25 CA repeats of the ERbeta gene had over a 6-fold increased risk of colon cancer (OR, 6.71; 95% CI, 2.89-15.6). Our results suggest that the ERbeta gene is more important than ERalpha in the etiology of colorectal cancer.     

Androgen receptor and prostate-specific antigen gene polymorphisms and breast cancer in African-American women.

Several previous studies have found the CAG repeat polymorphism in exon 1 of the androgen receptor (AR) gene to be associated with breast cancer risk among some groups of Caucasian and Asian women. In a population-based case-control study of 488 African-American women (239 cases and 249 controls), we examined this polymorphism along with a polymorphism (-158 G/A) in an androgen-regulated gene (PSA) whose expression has been correlated with breast cancer prognosis. Overall, we did not observe any significant association between the CAG repeat polymorphism and breast cancer risk. However, among women with a first-degree family history of breast cancer, longer CAG repeats were associated with a significantly increased risk. Women carrying at least one longer allele [(CAG)n > or = 22] had a 3-fold increased risk compared to those with two shorter alleles (odds ratio, 3.18; 95% confidence interval, 1.08-9.36). There was no significant association between the PSA gene polymorphism and breast cancer risk, nor was there significant gene-gene interaction. In summary, our results further support that shorter CAG repeats (stronger AR transactivation activity) may reduce the risk of breast cancer, at least among some groups of women. Our data, however, are unable to provide evidence that PSA is the pathway through which the protective effect of androgens operates.     

Polymorphic CAG/CAA repeat length in the AIB1/SRC-3 gene and prostate cancer risk: a population-based case-control study.

In an earlier report, we showed that a shorter CAG repeat length in the androgen receptor (AR) gene is associated with an increased risk of prostate cancer in China, the population with the lowest reported prostate cancer incidence in the world. Because AR coactivators enhance transactivation of AR, in this report we evaluated the relationship of a CAG/CAA repeat length polymorphism in the AIB1/SRC-3 gene (amplified in breast cancer gene 1, a steroid receptor coactivator and an AR coactivator) with prostate cancer risk in a population-based case-control study in China. Genomic DNA from 189 prostate cancer patients and 301 healthy controls was used for the PCR-based assay. The AIB1/SRC-3 CAG/CAA repeat length ranged from 24 to 32, with the most common repeat length being 29. Homozygous 29/29 and heterozygous 28/29 were the most common genotypes, with 44 and 30% of the controls harboring these genotypes, respectively. Relative to subjects homozygous for 29 CAG/CAA repeats (29/29 genotype), individuals with the <29/29 genotype had a nonsignificant 31% increased risk [odds ratio (OR), 1.31; 95% confidence interval (CI), 0.87-1.97], whereas those homozygous for the <29 allele had a significant 81% excess risk (OR, 1.81; 95% CI, 1.00-3.28). The combined effect of CAG repeat lengths in the AR and AIB1/SRC-3 genes was also evaluated. Relative to men with both the 29/29 genotype of the AIB1/SRC-3 gene and a long CAG repeat length (> or =23) in the AR gene, those with both the <29/<29 AIB1/SRC-3 genotype and a short CAG repeat length in the AR gene (<23) had a 2.8-fold risk (OR, 2.78; 95% CI, 1.24-6.26). Together, our data indicate that the CAG/CAA repeat length in the AIB1/SRC-3 gene may be associated with prostate cancer risk in Chinese men and that the combination of CAG/CAA repeat lengths in both the AIB1/SRC-3 and AR genes may provide a useful marker for clinically significant prostate cancer. Expanded studies in other populations are needed to confirm this association and the combined effect of AIB1/SRC-3 and other hormone-related genes in prostate cancer etiology.     

Androgen receptor polymorphisms: association with prostate cancer risk, relapse and overall survival.

Several reports have suggested that one or both of the trinucleotide repeat polymorphisms in the human androgen receptor (hAR) gene, (CAG)n coding for polyglutamine and (GGC)n coding for polyglycine, may be associated with prostate cancer risk; but no study has investigated their association with disease progression. We present here a study of both hAR trinucleotide repeat polymorphisms not only as they relate to the initial diagnosis but also as they are associated with disease progression after therapy. Lymphocyte DNA samples from 178 British Caucasian prostate cancer patients and 195 control individuals were genotyped by PCR for the (CAG)n and (GGC)n polymorphisms in hAR. Univariate Cox proportional hazard analysis indicated that stage, grade and GGC repeat length were individually significant factors associated with disease-free survival (DFS) and overall survival (OS). The relative risk (RR) of relapse for men with more than 16 GGC repeats was 1.74 (95% CI 1. 08-2.79) and of dying from any cause, 1.98 (1.13-3.45). Adjusting for stage and grade, GGC effects remained but were not significant (RR(DFS)= 1.60, p = 0.052; RR(OS)= 1.65, p = 0.088). The greatest effects were in stage T1-T2 (RR(DFS)= 3.56, 95% CI 1.13-11.21) and grade 1 (RR(DFS)= 6.47, 95% CI 0.57-72.8) tumours. No differences between patient and control allele distributions were found by odds-ratio analysis, nor were trends with stage or grade evident in the proportion of short CAG alleles. Non-significant trends with stage and grade were found in the proportion of short GGC alleles. The (GGC)n polymorphism in this population is a significant predictor of disease outcome. Since the (GGC)(n) effect is strongest in early-stage tumours, this marker may help forecast aggressive behaviour and could be used to identify those patients meriting more radical treatment.     

The CAG repeat polymorphism in the androgen receptor gene (AR) and its relationship to head and neck cancer

Sex hormones may play an important role in the tumorigenic process of the head and neck. The aim of our work was to investigate whether the androgen receptor (AR) CAG repeat polymorphism is associated with an increased relative risk for head and neck cancer. Genomic DNA from 103 male patients with head and neck carcinomas and 100 male controls were analyzed for the AR CAG polymorphism by PCR amplification and direct sequencing or denaturing polyacrilamide gel electrophoresis. Logistic regression analysis showed a significant association between CAG repeat length and risk of head and neck cancer in individuals with more than 20 CAG repeats [OR=2.54 (95% CI, 1.3-4.8)]. For the group of individuals with oral and laryngeal cancer the estimated relative risk was increased to 2.79 (95% CI, 1.2-6.3) and 3.06 (95% CI, 1.0-9.6), respectively, in men with CAG repeat length >20. These results suggest, for the first time, that shorter AR CAG repeat alleles have a protective effect for head and neck cancer development.     

Associations between androgen and Vitamin D receptor microsatellites and postmenopausal breast cancer.

We investigated the association between polymorphism in the androgen receptor (AR) and vitamin D receptor (VDR) genes and breast cancer risk in a large population-based case-control study of genetically homogenous Swedish women. We successfully determined both AR CAG(n) and VDR A(n) genotype in 1,502 women with invasive breast cancer and in 1,510 control women. We did not find any associations between AR or VDR microsatellite lengths and breast cancer when we used a priori determined cutoffs (/=22 repeats for AR and /=19 for VDR) to define long and short alleles. There was statistically significant interaction between VDR genotype and parity, such that women with two short alleles had a halved risk for breast cancer, irrespective of parity, compared with nulliparous women with two long alleles. Homozygosity for the long VDR allele was associated with a more advanced clinical stage at diagnosis. In exploratory analyses, we determined cutoffs based on visual inspection of distributions of allele lengths among cases and controls and found that women carrying two alleles with <20 AR CAG(n) repeats had an increased risk for breast cancer, odds ratio of 1.67 (95% confidence interval, 1.17-2.38), compared with those with two alleles with >/=20 repeats. Women carrying two VDR alleles with <21 A(n) were also at an increased risk, odds ratio of 1.26 (95% confidence interval, 1.04-1.51). Our data do not support major roles for AR or VDR polymorphism as breast cancer risk factors. However, we did find an interaction between VDR genotype and parity that remains to be corroborated.     

Polymorphic CAG repeat length within the androgen receptor gene: identification of a subgroup of patients with increased risk of ovarian cancer

The CAG repeat (CAGn) present in the N-terminal region of the androgen receptor (AR) inversely correlates with AR transactivation activity. The aim of this study was to investigate whether polymorphic variation in the CAGn length is associated with the risk of developing ovarian cancer. Using a case-control study design 121 women with histologically confirmed ovarian cancer and 100 controls (healthy women) were genotyped for AR-CAG length. No marked difference in the mean length of CAGn was observed between ovarian cancer patients and controls. However, when considering patients with positive personal or family history of tumor (PPFHT), the mean lengths of the long allele, the short allele and the average of the 2 alleles were longer than in the controls. Odds ratios (OR) and their corresponding 95% confidence intervals (CI) were computed after allowance for age. We observed an increase in the risk of ovarian cancer, in terms of OR, in women with CAGn >or=22 (OR=2.17, 95% CI:1.10-4.27). The increase of relative risk was particularly high in women with CAGn >or=22 belonging to the PPFHT group: OR=3.52 (95% CI 1.18-10.47). We also found a statistically significant trend (chi2 trend=4.91; p=0.03) towards an increased risk of ovarian cancer with increasing CAGn length (from or=26). Again, a strong association between increase in CAGn and risk of ovarian cancer was observed in PPFHT patients (chi2 trend=6.38; p=0.01). The results suggest that AR-CAG repeat length could play a role as modifier of the ovarian cancer risk conferred by highly penetrant genes rather than itself conferring a low risk.     

Allelic variants of aromatase and the androgen and estrogen receptors: toward a multigenic model of prostate cancer risk.

PURPOSE: The purpose of this study was to determine whether polymorphisms in the CAG repeat in exon 1 of the androgen receptor (AR), two intronic restriction sites in the estrogen receptor (ESR1 XbaI and ESR1 PvuII), and an Arg264Cy5 substitution in the aromatase gene (CYP19) contribute to prostate cancer risk. EXPERIMENTAL DESIGN: A case-control study was performed with 88 Caucasian prostate cancer patients and 241 Caucasian male controls. Logistic regression models were used to assess individual and joint contributions of genotypes to prostate cancer risk. RESULTS: For single polymorphisms, only the AR repeat number was significantly related to increased prostate cancer risk [age- and body mass index (BMI)-adjusted odds ratio (OR), 1.14; 95% confidence interval (CI), 1.04-1.25], suggesting a 14% increase in risk for each missing CAG repeat. When subjects were classified as either long (> or =23 AR CAG repeats) or short (<23 repeats) carriers, a significant increase in risk was also observed (age- and BMI-adjusted OR, 1.75; 95% CI, 1.05-2.95; P = 0.04). The aromatase C/T was associated with an increase in risk of borderline significance (age- and BMI-adjusted OR, 2.50; 95% CI, 0.99-6.28). When examining the effects of two polymorphisms on prostate cancer risk, homozygosity for the ESR1 XbaI restriction site together with a longer AR was more frequent among controls (32%) than cases (18%; age- and BMI-adjusted OR, 0.39; 95% CI, 0.19-0.78). The aromatase C/C genotype together with a longer AR was also more frequent among controls (55%) than cases (41%; age- and BMI-adjusted OR, 0.51; 95% CI, 0.30-0.89). CONCLUSIONS: Estrogen and aromatase may play a role in prostate cancer. A multigenic model of prostate cancer susceptibility is also supported.     

Androgen receptor exon 1 CAG repeat length and breast cancer in women before age forty years.

BACKGROUND: We conducted a population-based, case-control-family study to determine whether androgen receptor (AR) exon 1 polymorphic CAG repeat length (CAGn) was a risk factor for early-onset breast cancer in the Australian population. METHODS: Case subjects under 40 years of age at diagnosis of a first primary breast cancer and age-matched control subjects were interviewed to assess family history and other risk factors. AR CAGn length was determined for 368 case subjects and 284 control subjects. Distributions in the two groups were compared by linear and logistic regression, allowing adjustment for measured risk factors. All statistical tests were two-tailed. RESULTS: When analyzed as either a continuous or a dichotomous variable, there was no association between CAG, length and breast cancer risk, before or after adjustment for risk factors. Mean (95% confidence interval [CI]) CAGn lengths were 22.0 (21.8-22.2) for case subjects and 22.0 (21.7-22.3) for control subjects (P = .9). The frequency (95% CI) of alleles with 22 or more CAGn repeats was 0.531 (0.494-0.568) for case subjects and 0.507 (0.465-0.549) for control subjects (P = .4). After adjustment, the average effect on log OR (odds ratio) per allele was 0.16 (95% CI = -0.03 to 0.40; P = .2), and the effect of any allele was equivalent to an OR of 1.40 (95% CI = 0.94-2.09; P = .1). Stratification by family history also failed to reveal any association. Similar results were obtained when alleles were defined by other cutoff points. CONCLUSION: We found no evidence for an association between AR exon 1 CAGn length and breast cancer risk in women under the age of 40, despite having 80% power to detect modest effects.     

The joint effect of smoking and AIB1 on breast cancer risk in BRCA1 mutation carriers

Women with BRCA1 mutations are at an elevated risk for breast cancer. AIB1 (NCOA3/SRC3) genotype and smoking may alter this risk. We examined the differences in breast cancer risk by AIB1 polyglutamine repeat polymorphism and pre-diagnosis smoking habits for BRCA1 mutation carriers to determine if there was an interaction between smoking and AIB1 genotype. Multivariate Cox proportional hazards regression was used with 316 female BRCA1 mutation carriers to model breast cancer risk. Ever having smoked was associated with a decreased breast cancer risk [Hazard Ratio (HR) = 0.63, 95% CI, 0.47-0.87]. A dose-response relationship between number of pack-years smoked and breast cancer risk was also found for women who smoked <20 pack years of cigarettes (HR = 0.72, 95% CI, 0.52-1.00) and for women who smoked >/=20 pack years (HR = 0.41, 95% CI, 0.23-0.71; P for trend = 0.0007). Women with a 28 repeat allele for AIB1 had a significantly reduced risk of breast cancer (HR = 0.72, 95% CI, 0.51-1.00). Women who smoked >/=20 pack-years with a 28 repeat allele had an even greater reduced risk of breast cancer (HR = 0.19, 95% CI, 0.07-0.54) compared to women who were never smokers with no 28 allele. Since AIB1 appears to modulate the effect of endogenous hormones via the estrogen receptor, and smoking affects circulating hormone levels, these results support evidence that steroid hormones play an important role in breast carcinogenesis in BRCA1 mutation carriers, and suggest mechanisms for developing novel cancer prevention strategies for BRCA1 mutation carriers.     

CAG and GGC repeat polymorphisms in the androgen receptor gene and breast cancer susceptibility in BRCA1/2 carriers and non-carriers.

Variation in the penetrance estimates for BRCA1 and BRCA2 mutations carriers suggests that other genetic polymorphisms may modify the cancer risk in carriers. A previous study has suggested that BRCA1 carriers with longer lengths of the CAG repeat in the androgen receptor (AR) gene are at increased risk of breast cancer (BC). We genotyped 188 BRCA1/2 carriers (122 affected and 66 unaffected with breast cancer), 158 of them of Ashkenazi origin, 166 BC cases without BRCA1/2 mutations and 156 Ashkenazi control individuals aged over 56 for the AR CAG and GGC repeats. In carriers, risk analyses were conducted using a variant of the log-rank test, assuming two sets of risk estimates in carriers: penetrance estimates based on the Breast Cancer Linkage Consortium (BCLC) studies of multiple case families, and lower estimates as suggested by population-based studies. We found no association of the CAG and GGC repeats with BC risk in either BRCA1/2 carriers or in the general population. Assuming BRCA1/2 penetrance estimates appropriate to the Ashkenazi population, the estimated RR per repeat adjusted for ethnic group (Ashkenazi and non-Ashkenazi) was 1.05 (95%CI 0.97-1.17) for BC and 1.00 (95%CI 0.83-1.20) for ovarian cancer (OC) for CAG repeats and 0.96 (95%CI 0.80-1.15) and 0.90 (95%CI 0.60-1.22) respectively for GGC repeats. The corresponding RR estimates for the unselected case-control series were 1.00 (95%CI 0.91-1.10) for the CAG and 1.05 (95%CI 0.90-1.22) for the GGC repeats. The estimated relative risk of BC in carriers associated with > or =28 CAG repeats was 1.08 (95%CI 0.45-2.61). Furthermore, no significant association was found if attention was restricted to the Ashkenazi carriers, or only to BRCA1 or BRCA2 carriers. We conclude that, in contrast to previous observations, if there is any effect of the AR repeat length on BRCA1 penetrance, it is likely to be weak.     

Trinucleotide repeat polymorphisms in the androgen receptor gene and risk of ovarian cancer.

INTRODUCTION: Androgens may play a role in the development of ovarian cancers. Two trinucleotide repeat polymorphisms have been described in exon 1 of the androgen receptor (AR) gene that may affect its function. Previous studies of ovarian cancer and AR repeat polymorphisms have been inconsistent. METHODS: We analyzed CAG and GGC repeat length polymorphisms in the AR gene using data from a population-based case-control study of ovarian cancer that included 594 cases and 681 controls. Repeat lengths were determined by fluorescent DNA fragment analysis using ABI GeneScan software. Change point models were used to determine appropriate repeat length cutoff points by race (African American versus Caucasian) for both the shorter and longer CAG and GGC repeats. RESULTS: No relationship was observed between CAG repeat length and ovarian cancer among Caucasians. Among African Americans, having a short repeat length on either allele was associated with a 2-fold increase in ovarian cancer risk (age-adjusted odds ratio, 2.2; 95% confidence interval, 1.1-4.1). Having short CAG repeat lengths for both alleles was associated with a 5-fold increased risk for developing ovarian cancer (age-adjusted odds ratio, 5.4; 95% confidence interval, 1.4-1.7). No relationship with the GGC repeat length polymorphisms was observed. CONCLUSION: These results suggest that having a short CAG repeat length in AR increases ovarian cancer risk in African Americans. The failure to observe this relationship in Caucasians may be due to the rarity of such short CAG alleles in this population or could reflect racial differences in disease etiology.     

Androgen receptor exon 1 CAG repeat length and risk of ovarian cancer

Epidemiological studies indicate that ovarian cancer is an endocrine-related tumour. We conducted a case-control comparison to assess the androgen receptor (AR) exon 1 polymorphic CAG repeat length (CAG(n)) as a risk factor for epithelial ovarian cancer. AR CAG(n) was determined for 319 case subjects with ovarian adenocarcinoma and 853 unaffected control subjects (comprising 300 unrelated adult female monozygotic twins, and 553 adult females sampled randomly from the population using the electoral rolls). The CAG(n) distributions of case subjects and control subjects were compared as a continuum, and by dichotomising alleles according to different CAG(n) cut-points. Logistic regression was used to calculate age-adjusted odds ratio (OR) estimates. Analyzed as a continuous variable, there was no difference between case subjects and control subjects for the smaller, larger or average allele sizes of the CAG(n) genotype, before or after adjusting for age. The mean (95% CI) for the average CAG(n) was 22.0 (21.8-22.2) for case subjects and 22.0 (21.9-22.1) for control subjects (p>.9). Analysis of CAG(n) as a dichotomous variable showed no difference between case subjects and control subjects for the median cutpoint (>/= 22), or for another cut-point previously reported to act as a modifier of breast cancer risk (>/= 29). Our data provide no evidence for an association between ovarian cancer risk and the genotype defined by the AR exon 1 CAG(n) polymorphism, although we cannot exclude small effects, or threshold effects in a small subgroup.