Reproductive factors and breast cancer risk among BRCA1 or BRCA2 mutation carriers: Results from ten studies

Although reproductive factors are among the most well-established risk factors for breast cancer in the general population, it is still a matter for debate whether these factors act as risk modifiers among BRCA1 or BRCA2 mutation carriers. This meta-analysis is the first to be performed to determine the relationship between reproductive factors and breast cancer risk among BRCA1 and BRCA2 mutation carriers. We searched the PubMed database up to February 2013. A total of ten studies met the inclusion criteria. The results showed that the reproductive factors may be associated with breast cancer risk only among BRCA1 mutation carriers. No association was found between parity and breast cancer risk. Compared with women at the youngest age in the first-birth category, women in the oldest age category were at a 38% lower risk of breast cancer (RR = 0.62, 95%CI = 0.45–0.85). Breastfeeding for at least 1 or 2 years was associated with a 37% reduction in breast cancer risk (RR = 0.63, 95%CI = 0.46–0.86). Women at the oldest age in the menarche category were at a 34% lower risk of breast cancer (RR = 0.66, 95%CI = 0.53–0.81) than women in the youngest age category. However, none of the reproductive factors were associated with breast cancer risk among BRCA2 mutation carriers. In conclusion, late age at first birth, breastfeeding, and late age at menarche protect against breast cancer in BRCA1 mutation carriers only. Further studies are needed to explore the mechanisms.     

Anthropometric measures and risk of ovarian cancer among BRCA1 and BRCA2 mutation carriers

Studies conducted among women in the general population suggest that various anthropometric measures, including height and weight, may be associated with the risk of developing ovarian cancer. Whether such an association exists among women who carry a BRCA1 or BRCA2 mutation has not been evaluated. Thus, we investigated the association between height, weight, changes in body weight, and BMI, and the risk of developing ovarian cancer among 938 women carrying a BRCA1 or BRCA2 mutation. A matched case-control study was conducted in 469 pairs of women carrying a deleterious mutation in either BRCA1 (n = 403 pairs) or BRCA2 (n = 66 pairs). Information about height and weight at ages 18, 30, and 40 was collected from a questionnaire routinely administered to women during the course of genetic counseling. Conditional logistic regression was used to estimate the association between these body size measures and the risk of ovarian cancer. Height, weight, and BMI were not associated with the risk of ovarian cancer (P-trend ≥ 0.15). Also, there was no association between changes in body weight between ages 18-30, or ages 30-40, or ages 18-40 and the risk of ovarian cancer (P-trend ≥ 0.28). The results from this study suggest that height, weight, or weight gain do not influence the risk of ovarian cancer among carriers of a BRCA1 or BRCA2 mutation.     

Haplotype structure in Ashkenazi Jewish BRCA1 and BRCA2 mutation carriers

Three founder mutations in BRCA1 and BRCA2 contribute to the risk of hereditary breast and ovarian cancer in Ashkenazi Jews (AJ). They are observed at increased frequency in the AJ compared to other BRCA mutations in Caucasian non-Jews (CNJ). Several authors have proposed that elevated allele frequencies in the surrounding genomic regions reflect adaptive or balancing selection. Such proposals predict long-range linkage disequilibrium (LD) resulting from a selective sweep, although genetic drift in a founder population may also act to create long-distance LD. To date, few studies have used the tools of statistical genomics to examine the likelihood of long-range LD at a deleterious locus in a population that faced a genetic bottleneck. We studied the genotypes of hundreds of women from a large international consortium of BRCA1 and BRCA2 mutation carriers and found that AJ women exhibited long-range haplotypes compared to CNJ women. More than 50% of the AJ chromosomes with the BRCA1 185delAG mutation share an identical 2.1?Mb haplotype and nearly 16% of AJ chromosomes carrying the BRCA2 6174delT mutation share a 1.4?Mb haplotype. Simulations based on the best inference of Ashkenazi population demography indicate that long-range haplotypes are expected in the context of a genome-wide survey. Our results are consistent with the hypothesis that a local bottleneck effect from population size constriction events could by chance have resulted in the large haplotype blocks observed at high frequency in the BRCA1 and BRCA2 regions of Ashkenazi Jews.     

Frequency and carrier risk associated with common BRCA1 and BRCA2 mutations in Ashkenazi Jewish breast cancer patients.

Based on breast cancer families with multiple and/or early-onset cases, estimates of the lifetime risk of breast cancer in carriers of BRCA1 or BRCA2 mutations may be as high as 85%. The risk for individuals not selected for family history or other risk factors is uncertain. We determined the frequency of the common BRCA1 (185delAG and 5382insC) and BRCA2 (6174delT) mutations in a series of 268 anonymous Ashkenazi Jewish women with breast cancer, regardless of family history or age at onset. DNA was analyzed for the three mutations by allele-specific oligonucleotide hybridization. Eight patients (3.0%, 95% confidence interval [CI] 1.5%-5.8%) were heterozygous for the 185delAG mutation, two (0.75%, 95% CI 0.20-2.7) for the 5382insC mutation, and eight (3.0%, 95% CI 1.5-5.8) for the 6174delT mutation. The lifetime risk for breast cancer in Ashkenazi Jewish carriers of the BRCA1 185delAG or BRCA2 6174delT mutations was calculated to be 36%, approximately three times the overall risk for the general population (relative risk 2.9, 95% CI 1.5-5.8). For the 5382insC mutation, because of the low number of carriers found, further studies are necessary. The results differ markedly from previous estimates based on high-risk breast cancer families and are consistent with lower estimates derived from a recent population-based study in the Baltimore area. Thus, presymptomatic screening and counseling for these common mutations in Ashkenazi Jewish women not selected for family history of breast cancer should be reconsidered until the risk associated with these mutations is firmly established, especially since early diagnostic and preventive-treatment modalities are limited.     

BRCA1 and BRCA2 in hereditary breast cancer

The hereditary breast and ovarian cancer susceptibility genes, BRCA1 and BRCA2, have established roles in genome integrity maintenance and in the control of homologous recombination. Recent work has produced valuable insights into the mechanisms of action of the gene products. This review summarizes some of these advances, and attempts to place them in the context of known functions of the genes.     

Genetic variants associated with breast cancer risk for Ashkenazi Jewish women with strong family histories but no identifiable BRCA1/2 mutation

The ability to establish genetic risk models is critical for early identification and optimal treatment of breast cancer. For such a model to gain clinical utility, more variants must be identified beyond those discovered in previous genome-wide association studies (GWAS). This is especially true for women at high risk because of family history, but without BRCA1/2 mutations. This study incorporates three datasets in a GWAS analysis of women with Ashkenazi Jewish (AJ) homogeneous ancestry. Two independent discovery cohorts comprised 239 and 238 AJ women with invasive breast cancer or preinvasive ductal carcinoma in situ and strong family histories of breast cancer, but lacking the three BRCA1/2 founder mutations, along with 294 and 230 AJ controls, respectively. An independent, third cohort of 203 AJ cases with familial breast cancer history and 263 healthy controls of AJ women was used for validation. A total of 19 SNPs were identified as associated with familial breast cancer risk in AJ women. Among these SNPs, 13 were identified from a panel of 109 discovery SNPs, including an FGFR2 haplotype. In addition, six previously identified breast cancer GWAS SNPs were confirmed in this population. Seven of the 19 markers were significant in a multivariate predictive model of familial breast cancer in AJ women, three novel SNPs [rs17663555(5q13.2), rs566164(6q21), and rs11075884(16q22.2)], the FGFR2 haplotype, and three previously published SNPs [rs13387042(2q35), rs2046210(ESR1), and rs3112612(TOX3)], yielding moderate predictive power with an area under the curve (AUC) of the ROC (receiver-operator characteristic curve) of 0.74. Population-specific genetic variants in addition to variants shared with populations of European ancestry may improve breast cancer risk prediction among AJ women from high-risk families without founder BRCA1/2 mutations.     

Variation in cancer risks, by mutation position, in BRCA2 mutation carriers

Cancer occurrence in 164 families with breast/ovarian cancer and germline BRCA2 mutations was studied to evaluate the evidence for genotype-phenotype correlations. Mutations in a central portion of the gene (the "ovarian cancer cluster region" [OCCR]) were associated with a significantly higher ratio of cases of ovarian:breast cancer in female carriers than were mutations 5' or 3' of this region (P<.0001), extending previous observations. The optimal definition of the OCCR, as judged on the basis of deviance statistics, was bounded by nucleotides 3059-4075 and 6503-6629. The relative and absolute risks of breast and ovarian cancer associated with OCCR and non-OCCR mutations were estimated by a conditional likelihood approach, conditioning on the set of mutations observed in the families. OCCR mutations were associated both with a highly significantly lower risk of breast cancer (relative risk [RR] 0.63; 95% confidence interval (95% CI) 0.46-0.84; P=.0012) and with a significantly higher risk of ovarian cancer (RR = 1.88; 95% CI = 1.08-3.33; P=.026). No other differences in breast or ovarian cancer risk, by mutation position, were apparent. There was some evidence for a lower risk of prostate cancer in carriers of an OCCR mutation (RR = 0.52; 95% CI = 0.24-1.00; P=.05), but there was no evidence of a difference in breast cancer risk in males. By age 80 years, the cumulative risk of breast cancer in male carriers of a BRCA2 mutation was estimated as 6.92% (95% CI = 1.20%-38.57%). Possible mechanisms for the variation in cancer risk are suggested by the coincidence of the OCCR with the RAD51-binding domain.     

A computer model to simulate family history of breast/ovarian cancer in BRCA1 mutation carriers

The BRCA1 gene and its relationship to family history of breast/ovarian cancer are difficult to study in a population because of practical and ethical issues. The paucity of information on BRCA1 in the general population was a major theme in a recent review of genetic testing in Canada. We develop a simulation model to mimic genetic inheritance and cancer incidence in the family of someone with a germline BRCA1 mutation. Given someone's age and family structure, our model simulates his or her family history in three steps: (1) determine which family members have the mutation, (2) determine the ages of family members and (3) determine which family members have breast/ovarian cancer. Each step involves random variation. Some parameters in our model are estimated using local (British Columbia, Canada) population data. The breast/ovarian cancer risk associated with BRCA1 mutations is estimated using values published in the literature. An example is provided to illustrate the model's application. The model incorporates results from genetics, demography and epidemiology, but requires several additional assumptions. Research to address these assumptions is recommended.     

A systematic genetic assessment of 1,433 sequence variants of unknown clinical significance in the BRCA1 and BRCA2 breast cancer-predisposition genes

Mutation screening of the breast and ovarian cancer-predisposition genes BRCA1 and BRCA2 is becoming an increasingly important part of clinical practice. Classification of rare nontruncating sequence variants in these genes is problematic, because it is not known whether these subtle changes alter function sufficiently to predispose cells to cancer development. Using data from the Myriad Genetic Laboratories database of nearly 70,000 full-sequence tests, we assessed the clinical significance of 1,433 sequence variants of unknown significance (VUSs) in the BRCA genes. Three independent measures were employed in the assessment: co-occurrence in trans of a VUS with known deleterious mutations; detailed analysis, by logistic regression, of personal and family history of cancer in VUS-carrying probands; and, in a subset of probands, an analysis of cosegregation with disease in pedigrees. For each of these factors, a likelihood ratio was computed under the hypothesis that the VUSs were equivalent to an "average" deleterious mutation, compared with neutral, with respect to risk. The likelihood ratios derived from each component were combined to provide an overall assessment for each VUS. A total of 133 VUSs had odds of at least 100 : 1 in favor of neutrality with respect to risk, whereas 43 had odds of at least 20 : 1 in favor of being deleterious. VUSs with evidence in favor of causality were those that were predicted to affect splicing, fell at positions that are highly conserved among BRCA orthologs, and were more likely to be located in specific domains of the proteins. In addition to their utility for improved genetics counseling of patients and their families, the global assessment reported here will be invaluable for validation of functional assays, structural models, and in silico analyses.     

Contribution of BRCA1 germline mutation in patients with sporadic breast cancer

Hereditary artifacts in BRCA1 gene have a significant contributory role in familial cases of breast cancer. However, its germline mutational penetrance in sporadic breast cancer cases with respect to Pakistani population has not yet been very well defined. This study was designed to assess the contributory role of germline mutations of this gene in sporadic cases of breast cancer. 150 cases of unilateral breast cancer patients, with no prior family history of breast cancer and no other disorders or diseases in general with age range 35–75 yrs, were included in this study.Mutational analysis for hot spots on Exon 2, 3 and 13 of BRCA1 was done by using Single Strand Conformational Polymorphism (SSCP). Sequence analysis revealed five variants (missense) and one novel splice site mutation at exon 13. No germline mutation was observed on the remaining exons with respect sporadic breast cancer cases in Pakistani population. A vast majority of breast cancer cases are sporadic; the present study may be helpful for designing a better genetic screening tool for germline BRCA mutations in sporadic breast cancer patients of Pakistani population. Further studies involving a screening of entire coding region of BRCA1 is required to explore the merits of genetic diagnosis and counseling in breast cancer patients.     

Loss of nuclear BRCA1 protein staining in normal tissue cells derived from BRCA1 and BRCA2 mutation carriers

Enhanced genomic instability has been recently reported in normal cells derived from BRCA1/2 mutation carriers when placed in vitro in non-physiological stress conditions. We present here original data which help to explain the observed genomic instability. Leucocytes from BRCA1/2 mutation carriers, sporadic breast cancer patients and controls were prepared for BRCA1 immunocytochemistry. We show that BRCA1 containing nuclear dot like structures are detectable in about 80% of the leucocytes from controls and sporadic breast cancer patients, but are absent in the majority of normal cells from BRCA1 as well as BRCA2 mutation carriers (also in their normal breast cells). Our results thus indicate that the genomic instability observed in normal cells from BRCA1 and BRCA2 mutation carriers is associated with a down-regulation of nuclear BRCA1 protein accumulation in the dot like structures. These results suggest in addition that immunocytochemical or alternative molecular screening strategies might help to identify women with a high risk for breast (ovarian) cancer even when the underlying genetic defect remains undetectable.     

MCPH1 protein expression and polymorphisms are associated with risk of breast cancer

Microcephalin 1 (MCPH1) has a crucial role in the DNA damage response by promoting the expression of checkpoint kinase 1 (CHK1) and breast cancer susceptibility gene 1 (BRCA1). MCPH1 containing BRCT domain has been suggested as a tumor suppressor in breast and ovarian cancers. We analyzed the effect of both protein expression and MCPH1 polymorphisms in breast cancer patients. Low nuclear expression of microcephalin was present in 52.4% of breast cancers and was associated with allele T in rs2912010 (p = 0.046). However, cytoplasmic microcephalin expression increased with increasing grade (p = 0.010). An association between low nucleus microcephalin expression and allele T was identified in rs2912010 (p = 0.046). After data analysis, allele distribution of the MCPH1 polymorphisms was not different between breast cancer patients and healthy controls. But the polymorphism was associated with negative status for ER (rs2912010/C2302T; p = 0.032, rs1057090/C2358T; p = 0.027, rs2912016/C2494A; p = 0.024), and allele T in both rs2912010 and rs1057090 was associated with increasing tumor grade (rs2912010; p = 0.040, rs1057090; p = 0.043) in breast cancer. We are first to report that association of MCPH1 protein expression and its polymorphisms in breast cancer. The MCPH1 polymorphisms and protein expression were associated with tumorigenesis in breast cancer and may be a useful biomarker for identification of the aggressive types of breast cancer.     

Haplotype analysis of BRCA2 8765delAG mutation carriers in French Canadian and Yemenite Jewish hereditary breast cancer families

The BRCA2 8765delAG mutation was previously reported in hereditary breast cancer families of French Canadian and Yemenite Jewish descent. Haplotype analysis, using six microsatellite markers that span BRCA2 and two intragenic polymorphisms, was performed on 8765delAG mutation carriers to determine if there was evidence that the mutations were identical by descent. The alleles of the microsatellite markers most closely flanking BRCA2 (D13S1697 and D13S1701) were found to be identical in state in all the mutation carriers. However, the disease-associated allele of one of the intragenic markers differed between the Yemenite Jews and French Canadian families, indicating that the 8765delAG mutation has independent origins in these two geographically and ethnically distinct populations.     

BRCA1 and BRCA2 associated breast cancer and the roles of current modelling systems in drug discovery

For a drug candidate to be fully developed takes years and investment of hundreds of millions of dollars. There is no doubt that drug development is difficult and risky, but vital to protecting against devastating disease. This difficulty is clearly evident in BRCA1 and BRCA2 related breast cancer, with current treatment options largely confined to invasive surgical procedures, as well as chemotherapy and radiotherapy regimes which damage healthy tissue and can leave remnant disease. Consequently, patient survival and relapse rates are far from ideal, and new candidate treatments are needed. The preclinical stages of drug discovery are crucial to get right for translation to hospital beds. Disease models must take advantage of current technologies and be accurate for rapid and translatable treatments. Careful selection of cell lines must be coupled with high throughput techniques, with promising results trialled further in highly accurate humanised patient derived xenograft models. Traditional adherent drug screening should transition to 3D culture systems amenable to high throughput techniques if the gap between in vitro and in vivo studies is to be partially bridged. The possibility of organoid, induced pluripotent stem cell, and conditionally reprogrammed in vitro models is tantalising, however protocols are yet to be fully established. This review of BRCA1 and BRCA2 cancer biology and current modelling systems will hopefully guide the design of future drug discovery endeavours and highlight areas requiring improvement.     

BRCA1 and BRCA2 mutation analysis of 208 Ashkenazi Jewish women with ovarian cancer

Ovarian cancer is a component of the autosomal-dominant hereditary breast-ovarian cancer syndrome and may be due to a mutation in either the BRCA1 or BRCA2 genes. Two mutations in BRCA1 (185delAG and 5382insC) and one mutation in BRCA2 (6174delT) are common in the Ashkenazi Jewish population. One of these three mutations is present in approximately 2% of the Jewish population. Each mutation is associated with an increased risk of ovarian cancer, and it is expected that a significant proportion of Jewish women with ovarian cancer will carry one of these mutations. To estimate the proportion of ovarian cancers attributable to founding mutations in BRCA1 and BRCA2 in the Jewish population and the familial cancer risks associated with each, we interviewed 213 Jewish women with ovarian cancer at 11 medical centers in North America and Israel and offered these women genetic testing for the three founder mutations. To establish the presence of nonfounder mutations in this population, we also completed the protein-truncation test on exon 11 of BRCA1 and exons 10 and 11 of BRCA2. We obtained a detailed family history on all women we studied who had cancer and on a control population of 386 Ashkenazi Jewish women without ovarian or breast cancer. A founder mutation was present in 41.3% of the women we studied. The cumulative incidence of ovarian cancer to age 75 years was found to be 6.3% for female first-degree relatives of the patients with ovarian cancer, compared with 2.0% for the female relatives of healthy controls (relative risk 3.2; 95% CI 1.5-6.8; P=.002). The relative risk to age 75 years for breast cancer among the female first-degree relatives was 2.0 (95% CI 1.4-3.0; P=.0001). Only one nonfounder mutation was identified (in this instance, in a woman of mixed ancestry), and the three founding mutations accounted for most of the observed excess risk of ovarian and breast cancer in relatives.