No association between androgen or vitamin D receptor gene polymorphisms and risk of breast 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.

Microsatellite profile in hormonal receptor genes associated with breast cancer

Given that breast cancer is depending on multiple hormonal influences, the nuclear receptors, estrogen receptor alpha, estrogen receptor beta and androgen receptor, are candidates for cancer susceptibility markers. We conducted an association study in a case-control population (139 cases and 145 controls) by genotyping three potentially functional microsatellites (TA)n, (CA)n and (CAG)n in the ERa, ERb and AR genes respectively. For (CAG)n polymorphism, a significant difference was observed using a cut-off 15 repeats CAG between genotypes short-short/short-long/long-long in cases and control subjects (p = 0.009) and also between the distribution of short/long allele in the two groups of individuals (p = 0.001). Genotypes comprising one or two short (CAG)n sequences had higher risk of breast cancer compared to genotypes with two long allele (odds ratio = 1,93; confidence interval = 1.05-3.55; p = 0.03). No significant difference was observed in allele frequency or in short/long allele percentage for (CA)n or (TA)n polymorphism (cut-off 22 CA and 19 TA repeats), neither in genotype frequencies (short-short, short-long or long-long). When the three microsatellite genotype were taken in analysis, the profile short CA-long TA-short CAG could clearly discriminate between cases and controls (p = 0.006). Also, this combined genotype profile has greater predictive values for breast cancer than (CAG)n genotype alone (predictive positive value 57,1% versus 53,7% and predictive negative value 53% versus 23% respectively). Our results sustain a polygenic model of breast cancer with gene-gene interactions; combined effects of three low-risk polymorphisms conferred significant genetic predisposition. Genotyping hormonal receptor genes ERa, ERb and AR could be a useful genetic marker for defining disease risk.

Male-to-male transmission of X-linked Alport syndrome in a boy with a 47,XXY karyotype

Alport syndrome (AS) is a genetically heterogeneous renal hereditary disease. Male-to-male transmission has been considered fully indicative of autosomal dominant AS. We report a family with male-to-male transmission of X-linked AS due to an extra X chromosome of paternal origin in the proband. Linkage analysis excluded the autosomal loci and demonstrated segregation with the COL4A5 locus (Xq22.3). Sperm FISH analysis from his father detected an increased XY disomy. Mutation screening of the COL4A5 gene identified a splicing mutation, c.4688G>A. The proband and his paternal grandmother showed random X chromosome inactivation. However, a preferential expression of the aberrantly spliced transcript was detected in the proband when compared to his grandmother. This finding could explain why the AS phenotype of this 47,XXY boy resembles more an affected male than a female carrier. This is the first reported case of concurrence of Alport and Klinefelter syndromes.

Androgen receptor cytosine, adenine, guanine repeats, and haplotypes in relation to ovarian cancer risk

Biological and epidemiologic evidence suggest that androgen or its receptor may play a role in ovarian cancer pathogenesis. The most notable genetic factor influencing androgen receptor (AR) activity is the functional cytosine, adenine, guanine (CAG) repeat in which length is inversely proportional to its transactivational activity. Additional genetic variation due to single nucleotide polymorphisms in the AR gene may be captured through haplotypes. We genotyped the CAG microsatellite and six haplotype-tagging single nucleotide polymorphisms (rs962458, rs6152, rs1204038, rs2361634, rs1337080, rs1337082) of the androgen receptor gene in 987 ovarian cancer cases and 1,034 controls from a study conducted in New Hampshire and eastern Massachusetts between May 1992 and July 2003. We estimated haplotype frequencies and calculated odds ratios with 95% confidence intervals to evaluate the association between the haplotypes and the AR CAG microsatellite with ovarian cancer risk. We observed that carriage of two alleles with > or = 22 CAG repeats was associated with an increased risk of ovarian cancer compared with carriage of two alleles with <22 CAG repeats (covariate-adjusted odds ratios, 1.31; 95% confidence intervals, 1.01-1.69). Five common haplotypes in the AR gene were identified, but no association between these and ovarian cancer risk was observed. Our results suggest that possession of two long AR alleles (> or = 22 CAG repeats) may be associated with increased risk of ovarian cancer compared with women with two short AR alleles (<22 CAG repeats).

Gene variants for osteoporosis and their pleiotropic effects in aging

The prevalence of osteoporosis is raising worldwide as improving conditions of living and treatment of other common diseases continuously increases life expectancy. Thus, osteoporosis affects most women above 80 years of age and, at the age of 50, the lifetime risk of suffering an osteoporosis-related fracture approaches 50% in women and 20% in men. Numerous genetic, hormonal, nutritional and life-style factors contribute to the acquisition and maintenance of bone mass. Among them, genetic variations explain as much as 70% of the variance for bone mineral density (BMD) in the population. Dozens of quantitative trait loci (QTLs) for BMD have been identified by genome screening and linkage approaches in humans and mice, and more than 100 candidate gene polymorphisms tested for association with BMD and/or fracture. Sequence variants in the vitamin D receptor (VDR), collagen 1 alpha 1 chain (Col1A1), estrogen receptor alpha (ESR1), interleukin-6 (IL-6) and LDL receptor-related protein 5 (LRP5) genes were all found to be significantly associated with differences in BMD and/or fracture risk in multiple replication studies. Moreover, some genes, such as VDR and IL-6, were shown to interact with non-genetic factors, i.e. calcium intake and estrogens, to modulate BMD. Since these gene variants have also been associated with other complex disorders, including cancer and coronary heart disease, they may represent common genetic susceptibility factors exerting pleiotropic effects during the aging process.

Plasma 25-hydroxy vitamin D concentrations, vitamin D receptor genotype and breast cancer risk in a UK Caucasian population

Low levels of 25-hydroxy vitamin D (25(OH)D) and polymorphisms in the vitamin D receptor gene (VDR) have been found separately to increase risk of breast cancer. The aim of this study was to determine whether low 25(OH)D levels, alone and in combination with BsmI VDR genotype, increased breast cancer risk in a United Kingdom (UK) Caucasian population. Breast cancer patients (n=179) and control women (n=179) were recruited and 25(OH)D levels measured by enzyme-linked immunosorbent assay (ELISA). VDR genotype was determined by polymerase chain reaction (PCR) and restriction enzyme digest. Analysis showed that subjects with 25(OH)D levels <50 nM and the bb BsmI VDR genotype are 6.82 times more likely to have breast cancer than subjects with levels of 25(OH)D>50 nM and either the BB or Bb genotype (95% confidence interval (CI) 2.31-14.7, P<0.001). This study indicates that low levels of circulating 25(OH)D, both alone and in combination with BsmI VDR genotype, may increase risk of breast cancer in a UK Caucasian population.

Prevention of Hormone-Related Cancers: Breast Cancer

Carcinogenesis in the breast is a hormonally dependent process. Evidence implicating estrogen as a key breast carcinogen comes from various lines of investigation. Traditional epidemiologic studies demonstrate associations between estrogen exposure, both exogenous and endogenous, and increased breast cancer risk. Ongoing genetic epidemiologic studies also show associations between specific polymorphisms in estrogen-metabolizing genes and risk, albeit inconsistently. The application of these findings to the treatment and, more recently, the prevention of breast cancer has led to the development of agents that either (1) inhibit estrogen action at the estrogen receptor (selective estrogen receptor modulators (SERMs]); or (2) inhibit estrogen-synthesizing enzymes, thereby abrogating synthesis of this hormone (aromatase inhibitors). Large phase III trials have evaluated the ability of such agents to reduce the incidence of breast cancer in women at increased risk of the disease. The National Surgical Adjuvant Breast and Bowel Project (NSABP) P-1: Breast Cancer Prevention Trial (BCPT) demonstrated the superiority of the SERM tamoxifen to placebo in reducing breast cancer risk, leading to the Food and Drug Administration approval of tamoxifen for risk reduction. The implementation of tamoxifen for this indication has not become widespread in clinical practice, however, for a variety of reasons that we discuss. Results from the NSABP Study of Tamoxifen and Raloxifene, which compares the risk-reducing efficacy as well as toxicity of these two SERMs in a similar high-risk population, will be available in the near future. Based on promising data involving reduction of contralateral breast cancer risk in adjuvant studies, several aromatase inhibitors, including letrozole, anastrozole, and exemestane, are being incorporated into trials evaluating their efficacy as preventive agents in women at increased risk.

Vitamin D receptor gene polymorphism as an important modifier of positive family history related breast cancer risk

The association between vitamin D receptor (VDR) gene polymorphisms and diseases such as breast cancer, prostate cancer and osteoporosis has been extensively investigated during recent years. To date, several polymorphisms have been found in the VDR gene. In this Finnish case-control study, comprising 483 breast cancer patients and 482 healthy population controls, we investigated the association between altered breast cancer risk and two polymorphisms in the 3' end of the gene detectable with ApaI and TaqI restriction enzymes. A statistically significant difference was observed in the ApaI genotype distribution between cases and controls. Women with the VDR variant a allele containing genotypes showed a decreased risk for breast cancer [odds ratio (OR) 0.73, 95% confidence interval (CI) 0.54-0.98] compared to women with the AA genotype. This association was especially strong among women with a positive family history of breast cancer (OR 0.14, 95% CI 0.03-0.76). Moreover, there was a trend (P for trend = 0.0007) for decreased risk with increasing number of variant alleles. The lowest risk of breast cancer was seen for the women with the aa genotype (OR 0.03, 95% CI 0.003-0.31) compared to women with the AA genotype. A tendency of decreased risk of breast cancer was also observed for the TaqI T allele containing genotypes (Tt and TT) (OR 0.68, 95% CI 0.41-1.12), but because the distribution of Taql alleles in the controls missed the Hardy-Weinberg equilibrium (P = 0.01), we were unable to properly assess the potential impact of the TaqI polymorphism in breast cancer susceptibility. In conclusion, our results suggest that the VDR ApaI genotype may be an important modifier of individual breast cancer risk among Finnish women, especially if they have a positive family history of breast cancer.

A novel polymorphism in the 1A promoter region of the vitamin D receptor is associated with altered susceptibilty and prognosis in malignant melanoma

The association of Taq 1 and Fok 1 restriction fragment length polymorphisms of the vitamin D receptor with occurrence and outcome of malignant melanoma (MM), as predicted by tumour (Breslow) thickness, has been reported previously. We now report a novel adenine–guanine substitution −1012 bp relative to the exon 1a transcription start site (A-1012G), found following screening by single-stranded conformational polymorphism of this promoter region. There was a total of 191 MM cases , which were stratified according to conventional Breslow thickness groups, cases being randomly selected from each group to form a distribution corresponding to the known distribution of Breslow thickness in our area, and this population (n=176) was compared to 80 controls. The A allele was over-represented in MM patients and, with GG as reference, odds ratio (OR) for AG was 2.5, 95% confidence interval (CI) 1.1–5.7, (P=0.03) and AA 3.3, CI 1.4–8.1, (P=0.007). The outcome was known in 171 of 191 patients and the A allele was related to the development of metastasis, the Kaplan–Meier estimates of the probability of metastasis at 5 years being: GG 0%; AG 9%, CI 4–16%; AA 21%, CI 12–36%; (P=0.008), and to thicker Breslow thickness groups (P=0.04). The effect on metastasis was independent of tumour thickness and A-1012G may have predictive potential, additional to Breslow thickness. Neither the Fok 1 nor Taq 1 variants (f and t) were significantly related to the development of metastasis, although there was a strong relationship of fftt with the thickest Breslow thickness group (P=0.005). There was an interaction between the A-1012G and Fok 1 polymorphisms (P=0.025) and the Fok 1 variant enhanced the effect of the A allele of the A-1012G polymorphism on metastasis, the probability of metastasis for AAff at 5 years follow-up being 57%, CI 24–92%.

Vitamin D Receptor Gene Polymorphisms and Breast Cancer Risk

PURPOSE

The steroid hormone 1,25-dihydroxyvitamin D3 is thought to protect against breast cancer. The actions of 1,25-dihydroxyvitamin D3 are mediated via the vitamin D receptor (VDR), and a number of polymorphisms in the VDR gene have been identified. These result in distinct genotypes, some of which may alter susceptibility to breast cancer. We have investigated whether specific VDR gene polymorphisms are associated with breast cancer risk in a United Kingdom Caucasian population.

EXPERIMENTAL DESIGN

In a retrospective case-control study, female breast cancer patients (n = 398) and control women (n = 427) were recruited, and three VDR polymorphisms were determined.

RESULTS

The 3' VDR polymorphisms BsmI and variable-length poly(adenylate) sequence were both significantly associated with breast cancer risk; odds ratios (adjusted for age menopausal status and hormone replacement therapy usage) for bb genotype versus BB genotype = 1.92 (95% confidence interval, 1.20-3.10; P < 0.01) and for LL versus SS = 1.94 (95% confidence interval, 1.20-3.14; P < 0.01). A 5' VDR gene variant, FokI, was not associated with breast cancer risk when analyzed in isolation (P > 0.05). However, FokI did modulate the increased risk associated with the bb/LL genotype such that possession of one or more F alleles together with the bb/LL genotype augmented breast cancer risk. Furthermore, the highest proportion of bb and FFLL/FfLL genotypes occurred in women with metastatic breast cancer.

CONCLUSIONS

VDR polymorphisms are associated with breast cancer risk and may be associated with disease progression. Additional investigations into how different genotypes may affect the functional mechanisms of the VDR will provide a better strategy for identifying women at risk of breast cancer and for developing improved treatments.

Androgen and vitamin D receptor expression in archival human breast tumors

BACKGROUND

The present study was undertaken for quantitation of androgen (AR) and vitamin D (VDR) receptor expression in human male and female breast tumors by flow cytometry.

METHODS

Nuclei isolated from sections of paraffin-embedded tumors by pepsin digestion were treated for antigen unmasking and incubated with antibodies to AR and VDR. Flow cytometric analysis was used to determine the percentage of receptor-positive nuclei with fluorescence greater than 95% of the isotype nuclei. Mean log fluorescence channel values were used for comparing antigen density of the isotype and the antibody-treated nuclei.

RESULTS

Six of 23 female breast tumors had aneuploid DNA content. Nineteen of 20 estrogen receptor-positive female tumors by immunohistochemical analysis (IHC) were also AR positive by flow analysis. Aneuploid subpopulations had higher percentages of AR-positive nuclei than did diploid populations. Eight of 33 male breast tumors had aneuploid DNA content. Twenty-three of 33 male breast tumors were AR positive by flow analysis compared with six that were AR positive by IHC. Six AR-positive (IHC) male tumors were also AR positive by flow analysis. VDR expression was higher in diploid female tumors than in aneuploid tumors.

CONCLUSIONS

Lack of a strong correlation between IHC and flow analysis may be due to differences in criteria used for identification of receptor-positive and -negative tumors by the two methods.

Polymorphism in the Androgen Receptor and Mammographic Density in Women Taking and Not Taking Estrogen and Progestin Therapy

There is some evidence that women with a higher number of CAG repeat lengths on the androgen receptor (AR) gene have increased breast cancer risk. We evaluated the association between AR-CAG repeat length and mammographic density, a strong breast cancer risk factor, in 404 African-American and Caucasian breast cancer patients. In postmenopausal estrogen progestin therapy users, carriers of the less active AR-CAG had statistically significantly higher mean percentage of density (41.4%) than carriers of the more active AR-CAG (25.7%; P = 0.04). Our results raise the question of whether the number of AR-CAG repeats predicts breast cancer risk in estrogen progestin therapy users.

Approaches to evaluating the association of vitamin D receptor gene polymorphisms with breast cancer risk

The steroid hormone 1,25 dihydroxyvitamin D3 is thought to protect against breast cancer. Its actions are mediated via the vitamin D receptor (VDR) and a number of polymorphisms in the VDR gene have been identified, some of which may alter susceptibility to breast cancer. This study has investigated whether specific VDR gene polymorphisms are associated with breast cancer risk in a UK Caucasian population. Female breast cancer patients (n = 313) and control women with a negative screening mammogram (n = 410) were recruited and their VDR polymorphisms were determined. The 3' VDR polymorphism BsmI was significantly associated with breast cancer risk; odds ratio bb vs. BB genotype = 1.79 (95% CI, 1.12-2.86; P = 0.0221). In addition, over 70% of seven commonly used breast cancer cell lines were found to have the at-risk genotype bb. The 5' FokI gene variant was not associated with breast cancer risk. Further investigations into how these different genotypes may affect the functional mechanisms of the VDR will provide a better strategy for identifying women at risk of breast cancer and for developing improved treatments.

Vitamin D-3 receptor as a target for breast cancer prevention

The vitamin D-3 receptor (VDR) is a nuclear receptor that modulates gene expression when complexed with its ligand 1-alpha,25-dihydroxycholecalciferol [1,25(OH)(2)-D(3)], which is the biologically active form of vitamin D-3. The cellular effects of VDR signaling include growth arrest, differentiation and/or induction of apoptosis, which indicate that the vitamin D pathway participates in negative-growth regulation. Although much attention has been directed in recent years toward the development of synthetic vitamin D analogs as therapeutic agents for a variety of human cancers including those derived from the mammary gland, studies on vitamin D as a chemopreventive agent for breast cancer have been quite limited. The VDR is expressed in normal mammary gland, where it functions to oppose estrogen-driven proliferation and maintain differentiation; this suggests that 1,25(OH)(2)-D(3) participates in negative-growth regulation of mammary epithelial cells. Furthermore, preclinical studies show that vitamin D compounds can reduce breast cancer development in animals, and human data indicate that both vitamin D status and genetic variations in the VDR may affect breast cancer risk. Collectively, findings from cellular, molecular and population studies suggest that the VDR is a nutritionally modulated growth-regulatory gene that may represent a molecular target for chemoprevention of breast cancer.

The role of androgens and polymorphisms in the androgen receptor in the epidemiology of breast cancer

Testosterone binds to the androgen receptor in target tissue to mediate its effects. Variations in testosterone levels and androgen receptor activity may play a role in the etiology of breast cancer. Here, we review the epidemiologic evidence linking endogenous testosterone to breast cancer risk. Paradoxically, results from observational studies that have examined polymorphisms in the androgen receptor suggest that the low-activity androgen receptor increases breast cancer risk. We review the quality of this evidence and conclude with a discussion of how the androgen receptor and testosterone results coincide.

Androgen receptor CAG repeat length in Jewish Israeli women who are BRCA1/2 mutation carriers: association with breast/ovarian cancer phenotype

BRCA1/2 mutation carriers are at an increased risk for developing breast and/or ovarian cancer. Yet, the genetic and environmental factors that govern the phenotypic expression of mutant BRCA1/2 alleles remain elusive. The CAG repeat within exon 1 of the androgen receptor (AR) gene is reportedly associated with breast cancer phenotype in BRCA1 mutation carriers. Two hundred and twenty seven BRCA1/2 mutation carriers were genotyped for the polymorphic AR CAG repeat, and allele size was correlated with breast/ovarian cancer morbidity parameters. Of 227 BRCA1/2 carriers, 169 were BRCA1 mutation carriers and 58 carried a BRCA2 mutation, 149 had breast and/or ovarian cancer and 78 were asymptomatic mutation carriers. The mean age at diagnosis in women with either or both neoplasms was 46.7+/-11.2 years, and that of the asymptomatic group - 45.8+/-9.4 years, a statistically insignificant difference. The AR CAG repeat ranged from eight to 28 in all tested women, and the mean number of the repeats were not statistically different between affected (18.3+/-2.4) and asymptomatic mutation carriers (18.6+/-2.1). The AR CAG repeat among patients with early onset (<42 years) breast cancer was significantly shorter (17.5+/-2.3) compared with asymptomatic individuals (18.6+/-2.1) (P<0.01), and the shorter allele - the younger the age at diagnosis. There is no conclusive evidence of association between AR CAG repeat size and breast or ovarian cancer risk in Jewish BRCA1/2 mutation carriers. A small effect of a short AR CAG allele size on breast cancer at early age (<42 years) cannot be excluded.

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

PURPOSE

Previous reports have suggested that polymorphism in the vitamin D receptor (VDR) gene is associated with sporadic breast cancer, but there is controversy among different authors and ethnic groups. The purpose of this study was to determine whether polymorphism in the VDR gene might also influence breast cancer risk in Taiwan, a country with a low incidence of breast cancer.

METHODS

Polymorphisms in the end of the VDR gene were genotyped for 34 Taiwanese women with sporadic breast cancer, 46 with benign breast tumors and 169 cancer-free female cohort controls.

RESULTS

The ApaI, TaqI, and BsmI polymorphisms in the 3' end of the VDR gene were associated with breast cancer risk, with a trend for increasing risk with increased numbers of BsmI B alleles and ApaI AA genotypes. When the allele frequencies of BsmI polymorphism were compared among the three populations, a significant difference was observed (chi2 = 13.684, df = 4, p = 0.0084). The OR of the Aa genotype was 0.333 (95% CI = 0.1 14-0.978) and that of the aa genotype was 0.515 (95% CI = 0.190-1.398). These data indicate that the AA genotype may be associated with an increased risk of breast cancer, while the Aa genotype tends to be associated with decreased risk. The TaqI polymorphism was not associated with breast cancer risk in this study.

CONCLUSION

These results suggest that polymorphic variation in or near the 3' end of the VDR gene may influence breast cancer risk in Taiwanese women and justifies further investigation of the role of VDR for sporadic breast cancer in low-incidence areas. These findings also should help when designing targeted therapy.

Androgen receptor exon 1 CAG repeat length and risk of hepatocellular carcinoma in women

The androgen receptor (AR) gene is localized on chromosome X, and shorter CAG repeats in exon 1 of the AR gene were recently suggested to increase hepatitis B virus (HBV)-related hepatocellular carcinoma (HCC) risk among men. To examine whether the relationship between the AR-CAG repeats and HCC was also evident among women, we conducted a case-control study in Taiwan. The number of AR-CAG repeats was determined for 238 women with HCC and 354 unrelated control subjects (comprising 188 first-degree and 166 nonbiological relatives) selected from female relatives of patients with HCC. Women harboring 2 AR alleles with more than 23 CAG repeats had an increased risk of HCC (age-adjusted odds ratio [OR], 1.82; 95% CI, 1.06-3.14), compared with women with only short alleles or a single long allele. The association between harboring 2 AR alleles containing longer CAG repeats and HCC was more striking among HBV carriers (age-adjusted OR for more than 22 repeats, 2.23; 95% CI, 1.14-4.34) and particularly prominent among HBV carriers under age 53 years (age-adjusted OR, 3.16; 95% CI, 1.13-8.82). When CAG repeats were analyzed as a continuous variable, the increase in HCC risk associated with each incremental repeat in the shorter of 2 alleles in a given genotype was statistically significant among women with a first-degree relative with HCC (age-adjusted OR, 1.18; 95% CI, 1.01-1.37). No such relationship was detected among women without the family history. In conclusion, our observations suggest that the AR-CAG alleles may contribute to HCC predisposition among women through a mechanism different from that for men.

Genes other than BRCA1 and BRCA2 involved in breast cancer susceptibility

This review focuses on genes other than the high penetrance genes BRCA1 and BRCA2 that are involved in breast cancer susceptibility. The goal of this review is the discovery of polymorphisms that are either associated with breast cancer or that are in strong linkage disequilibrium with breast cancer causing variants. An association with breast cancer at a 5% significance level was found for 13 polymorphisms in 10 genes described in more than one breast cancer study. Our data will help focus on the further analysis of genetic polymorphisms in populations of appropriate size, and especially on the combinations of such polymorphisms. This will facilitate determination of population attributable risks, understanding of gene-gene interactions, and improving estimates of genetic cancer risks.

Androgens and mammary growth and neoplasia

OBJECTIVE

Evaluation of current clinical, experimental, genetic, and epidemiological data pertaining to the role of androgens in mammary growth and neoplasia.

DESIGN

Literature review.

SETTING

National Institutes of Health.

SUBJECT(S)

Recent, basic, clinical, and epidemiological studies.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Effects of androgens on mammary epithelial proliferation and/or breast cancer incidence.

RESULT(S)

Experimental data derived from rodents and cell lines provide conflicting results that appear be strain- and cell line-dependent. Epidemiologic studies have significant methodological limitations and provide inconclusive results. The study of molecular defects involving androgenic pathways in breast cancer is in its infancy. Clinical and nonhuman primate studies, however, suggest that androgens inhibit mammary epithelial proliferation and breast growth and that conventional estrogen treatment suppresses endogenous androgens.

CONCLUSION(S)

Abundant clinical evidence suggests that androgens normally inhibit mammary epithelial proliferation and breast growth. Suppression of androgens by conventional estrogen treatment may thus enhance estrogenic breast stimulation and possibly breast cancer risk. Clinical trials to evaluate the impact of combined estrogen and androgen hormone replacement regimens on mammary gland homeostasis are needed to address this issue.

Modifiers of risk of hereditary breast and ovarian cancer

Hereditary breast and ovarian cancer is among the most commonly encountered adult genetic disease, and it is increasingly important that geneticists, oncologists, surgeons and gynaecologists are aware of the issues regarding risk assessment, prevention and management of women with inherited susceptibility to cancer. Genetic risk can be modified by external factors, but what are these factors, and how might our knowledge of them help us to better define the risks for individual women and to develop strategies for cancer prevention?

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.

Vitamin D receptor gene polymorphisms are associated with breast cancer risk in a UK Caucasian population

There is increasing evidence that vitamin D can protect against breast cancer. The actions of vitamin D are mediated via the vitamin D receptor (VDR). We have investigated whether polymorphisms in the VDR gene are associated with altered breast cancer risk in a UK Caucasian population. We recruited 241 women following a negative screening mammogram and 181 women with known breast cancer. The VDR polymorphism Bsm I, an intronic 3' gene variant, was significantly associated with increased breast cancer risk: odds ratio bb vs BB genotype = 2.32 (95% CI, 1.23-4.39). The Bsm I polymorphism was in linkage disequilibrium with a candidate translational control site, the variable length poly (A) sequence in the 3' untranslated region. Thus, the 'L' poly (A) variant was also associated with a similar breast cancer risk. A 5' VDR gene variant, Fok I, was not associated with breast cancer risk. Further investigations into the mechanisms of interactions of the VDR with other environmental and/or genetic influences to alter breast cancer risk may lead to a new understanding of the role of vitamin D in the control of cellular and developmental pathways.

Receptor polymorphisms and diseases

The aim of our review is to summarize common genetic variations of some receptors associated with clinical consequences, which were not outlined in the previous special issue of this journal. Because of the multiple pathomechanisms of diseases, a set of genetic variation can play a role in the development of pathological conditions. From the data available three articles would merit a greater interest. In systemic lupus erythematosus the associations related to some polymorphisms of Fc-, tumor necrosis factor (TNF) alpha- and interferon receptor may explore new autoimmunological and inflammatorical pathomechanisms. In the endocrinology, the androgen receptor repeat polymorphism will exert significant aspects in the development of prostate cancer. The pleoitropic responsibility of vitamin D3 receptor polymorphism in the pathogenesis of immunological disorders (primary biliary cirrhosis, inflammatory bowel disease, type 1 diabetes mellitus) and of malignancies (malignant melanoma, breast cancer) shed light on the importance of common nuclear receptors. Nevertheless, in the future studies a more consistent approach minimizing requirement bias in the selection of patients will approve our understanding the role of genetic influence on the pathogenesis of diseases.