Major Breast Cancer Susceptibility Genes Research Articles

Next generation sequencing analysis of BRCA1 and BRCA2 identifies novel variations in breast cancer

Mutations in two major breast cancer susceptibility genes, BRCA1 and BRCA2, have been identified to be the most important predisposing factors for the development of breast cancer. Thus, BRCA1/2 testing is a well-established method of choice for the assessment of developing breast cancer. Accordingly, here we aimed to report novel BRCA1/2 variations and distribution of previously known mutations and their association with the clinical course of breast cancer disease. A total of 287 breast cancer patients were enrolled from January 2017 through December 2019. Of these patients, 50 of them were identified to be positive for BRCA1/2. Next Generation Sequencing analysis was performed for the screening of exonic and intronic variations of BRCA1/BRCA2 genes. Notably, novel variations of 4448 G > A (Ser1843Asn) in BRCA1, and 982dupA (Thr328AspfsTer) and 7588C > T (Gln2530Ter) in BRCA2 gene were identified. The most common variations in BRCA1 gene were 5152 + 66G > A, 442-34C > T and 5266dupC. In BRCA2 gene, the most common variations were 9097dupA, 67 + 1G > A and 1114A > C. Novel variations of BRCA1 and BRCA2 genes were identified in breast cancer and might be useful predisposing factors in breast cancer diagnosis.

Cancer Risks Associated With Germline PALB2 Pathogenic Variants: An International Study of 524 Families.

To estimate age-specific relative and absolute cancer risks of breast cancer and to estimate risks of ovarian, pancreatic, male breast, prostate, and colorectal cancers associated with germline PALB2 pathogenic variants (PVs) because these risks have not been extensively characterized. We analyzed data from 524 families with PALB2 PVs from 21 countries. Complex segregation analysis was used to estimate relative risks (RRs; relative to country-specific population incidences) and absolute risks of cancers. The models allowed for residual familial aggregation of breast and ovarian cancer and were adjusted for the family-specific ascertainment schemes. We found associations between PALB2 PVs and risk of female breast cancer (RR, 7.18; 95% CI, 5.82 to 8.85; P = 6.5 × 10-76), ovarian cancer (RR, 2.91; 95% CI, 1.40 to 6.04; P = 4.1 × 10-3), pancreatic cancer (RR, 2.37; 95% CI, 1.24 to 4.50; P = 8.7 × 10-3), and male breast cancer (RR, 7.34; 95% CI, 1.28 to 42.18; P = 2.6 × 10-2). There was no evidence for increased risks of prostate or colorectal cancer. The breast cancer RRs declined with age (P for trend = 2.0 × 10-3). After adjusting for family ascertainment, breast cancer risk estimates on the basis of multiple case families were similar to the estimates from families ascertained through population-based studies (P for difference = .41). On the basis of the combined data, the estimated risks to age 80 years were 53% (95% CI, 44% to 63%) for female breast cancer, 5% (95% CI, 2% to 10%) for ovarian cancer, 2%-3% (95% CI females, 1% to 4%; 95% CI males, 2% to 5%) for pancreatic cancer, and 1% (95% CI, 0.2% to 5%) for male breast cancer. These results confirm PALB2 as a major breast cancer susceptibility gene and establish substantial associations between germline PALB2 PVs and ovarian, pancreatic, and male breast cancers. These findings will facilitate incorporation of PALB2 into risk prediction models and optimize the clinical cancer risk management of PALB2 PV carriers.

Non-Coding Variants in BRCA1 and BRCA2 Genes: Potential Impact on Breast and Ovarian Cancer Predisposition

BRCA1 and BRCA2 are major breast cancer susceptibility genes whose pathogenic variants are associated with a significant increase in the risk of breast and ovarian cancers. Current genetic screening is generally limited to BRCA1/2 exons and intron/exon boundaries. Most identified pathogenic variants cause the partial or complete loss of function of the protein. However, it is becoming increasingly clear that variants in these regions only account for a small proportion of cancer risk. The role of variants in non-coding regions beyond splice donor and acceptor sites, including those that have no qualitative effect on the protein, has not been thoroughly investigated. The key transcriptional regulatory elements of BRCA1 and BRCA2 are housed in gene promoters, untranslated regions, introns, and long-range elements. Within these sequences, germline and somatic variants have been described, but the clinical significance of the majority is currently unknown and it remains a significant clinical challenge. This review summarizes the available data on the impact of variants on non-coding regions of BRCA1/2 genes and their role on breast and ovarian cancer predisposition.

Mismatch Repair Polymorphisms as Markers of Breast Cancer Prevalence in the Breast Cancer Family Registry.

Major breast cancer susceptibility genes involved in DNA repair, including BRCA1 and BRCA2, have been identified. However, mutations in these genes account for only 5-10% of identified breast cancer cases. Additional DNA repair pathway genes may also contribute to susceptibility. We investigated the association between 12 single nucleotide polymorphisms (SNPs) in mismatch repair (MMR) genes and breast cancer risk among 313 sister-sets enrolled in the New York site of the Breast Cancer Family Registry (BCFR) (n=744) using conditional logistic regression analysis. An increase in breast cancer risk was observed for women with the MUTYH_rs3219489 variant allele (odds ratio (OR)=2.23, 95% confidence interval (CI)=1.10-4.52) and for women with the MSH2_rs2303428 variant allele (OR=1.73, 95% CI=1.00-2.99). Deficiencies in DNA repair pathways, such as MMR, have implications for the onset of familial breast cancer.

Screening of HELQ in breast and ovarian cancer families

Several high and moderate risk alleles have been identified for breast and ovarian cancer predisposition and most of them encode proteins that function in DNA repair. A prospective candidate for breast and ovarian cancer susceptibility is the HELQ helicase that has a role in the resolution of DNA interstrand cross-links. HELQ interacts with the RAD51 paralog complex BCDX2. Two components of the complex, RAD51C and RAD51D, increase the risk of ovarian cancer especially, and the other two, RAD51B and XRCC2 have been associated with breast cancer risk. To investigate the role of HELQ in cancer predisposition, we screened the gene for germline variation in 185 Finnish breast or ovarian cancer families and performed haplotype analyses for 1517 breast cancer cases, 308 ovarian cancer cases, and 1234 population controls using five common polymorphisms at the HELQ gene locus. No truncating mutations were identified among the families. One putatively pathogenic missense mutation c.1309A>G was identified but no additional carriers were observed in the subsequent genotyping of 332 familial breast or ovarian cancer patients. Furthermore, the haplotype distribution did not differ between breast or ovarian cancer cases and population controls. Our results indicate that HELQ is not a major breast and ovarian cancer susceptibility gene in the Finnish population. However, we cannot rule out rare risk-variants in the Finnish or other populations and larger datasets are needed to further assess the role of HELQ especially in ovarian cancer predisposition.

The CHEK2 1100delC allelic variant is not present in familial and sporadic breast cancer cases from Moroccan population.

PurposeThe cell-cycle checkpoint kinase 2 (CHEK2) is an important signal transducer of cellular responses to DNA damage, whose defects has been associated with increased risk for breast cancer. The CHEK2 1100delC mutation has been reported to confer a twofold increased risk of breast cancer among carriers. The frequency of the mutation varies among populations. The highest frequency has been described in Northern and Eastern European countries. However, the 1100delC mutation has been investigated in different case-control studies and none in Moroccan population. The aim of this study was to evaluate the prevalence of this variant and determine its contribution to the development of breast cancer in sporadic cases and also in members of breast cancer families who tested negative or positive for a deleterious mutation in BRCA1/BRCA2.MethodsIn this case-control study we performed the CHEK2 1100delC mutation analysis by ASO-PCR in 134 breast cancer patients and 114 unaffected control individuals. Most of these families had several cases of breast cancer or ovarian cancer (or both).ResultsNo CHEK2 1100delC mutations were detected in any of 134 individuals, including 59 women diagnosed with breast cancer at an early age (<40 years), 10 women with bilateral breast cancer, and 6 women with ovarian cancer.ConclusionOur preliminary genetic analysis are consistent with the reported very low frequency of CHEK2 1100delC mutation in North American populations (compared with Northern Europe), rendering CHEK2 1100delC such as an unlikely to be major breast cancer susceptibility genes.

Analysis of PTEN in two BRCA1 and BRCA2 wild-type familial breast cancer patients.

Sir, Our study was designed to sequence the entire exonic regions and intronic junctions of the BRCA1, BRCA2, and PTEN genes with regard to identifying the influence of PTEN mutations in two Iranian families with familial breast cancer and BRCA1/2 wild-type genes [Figure 1]. Figure 1 Pedigrees of the two families with familial breast cancer carrying new germline sequence variants in the PTEN gene: One deletion (del T IVS4-29) and one single-nucleotide substitution (IVS2+65 G>A) Mutations in particular sets of genes are associated with an increased risk of hereditary breast and ovarian cancer (HBOC). These genes are categorized into three groups according to their impact on cancer susceptibility. The first group leading to elevated breast cancer risk (40% up to 85%)[1] with mutations of high penetrance include BCRA1, BCRA2, TP53, PTEN, and STK11.[2] PTEN mutations, as a rare but high penetrance mutation, are considered following the two major known breast cancer susceptibility genes, BRCA1 and BRCA2, in HBOC development.[3] Human genomic PTEN gene locus on chromosome 10q23.3 contains 9 exons encoding a 5.5 kb messenger RNA that has a 403 amino acid open reading frame.[4] Whole gene sequencing was done for three genes in these families. The BRCA1 and BRCA2 in the proband of the families were normal, and no germline abnormality was found in these two genes that are mainly responsible for familial breast cancer. However, two new germline sequence variants were detected in the PTEN gene: One deletion (del T IVS4-29) and one single-nucleotide substitution (IVS2+65 G>A) [Figure ​[Figure2a2a and ​andb].b]. Both new changes found in the PTEN gene were analyzed by the two servers NetGene 2 and alternative splice site predictor. Del T IVS4-29 change was impositioned in NetGene 2 site, the 3’ splice site acceptor changed in the consensus sequences, but did not delete the consensus sequences. The IVS2+65 G>A variation did not cause a new change in splicing site. Figure 2 (a) Heterozygous IVS2+65 G>A of the PTEN gene. (b) Heterozygous del IVS4-29 of the PTEN gene Despite new achievements in this area, many factors leading to breast cancer predisposition are still unknown, and thus need to be identified with further investigations. All the investigations to promote strategies of early cancer diagnosis, which is critical for the survival of affected individuals, might be advantageous. As the main mechanism for activating the PTEN protein is proteasomal degradation,[5] any changes in protein structure influence the integral role of it. The specific variations that we detected may make some mute changes in the protein interactions which may prevent it from performing its task. It can be cleared by the study of protein structure in future investigations. To the best of our knowledge, the study we present here is the first analysis of the PTEN gene in BRCA1 and BRCA2 wild-type breast and/or ovarian cancer in Iranian families. Financial support and sponsorship This work was supported by grants from Iran University of Medical Sciences project number 1021. Conflicts of interest There are no conflicts of interest.

BRCA1, a 'complex' protein involved in the maintenance of genomic stability.

BRCA1 is a major breast and ovarian cancer susceptibility gene, with mutations in this gene predisposing women to a very high risk of developing breast and ovarian tumours. BRCA1 primarily functions to maintain genomic stability via critical roles in DNA repair, cell cycle checkpoint control, transcriptional regulation, apoptosis and mRNA splicing. As a result, BRCA1 mutations often result in defective DNA repair, genomic instability and sensitivity to DNA damaging agents. BRCA1 carries out these different functions through its ability to interact, and form complexes with, a vast array of proteins involved in multiple cellular processes, all of which are considered to contribute to its function as a tumour suppressor. This review discusses and highlights recent research into the functions of BRCA1-related protein complexes and their roles in maintaining genomic stability and tumour suppression.

Made-to-measure medicine: BRCA and gynaecological cancer

20 years have passed since the discovery of the major breast cancer susceptibility gene, BRCA1. Extraordinary progress has been made in the understanding of how BRCA1 and its associated proteins function, and the clinical consequences of malfunctioning BRCA proteins are now evident.1,2 The initial concerns3 about the risks of genetic testing for women carrying mutations in BRCA1 and BRCA2 seem to have receded. Moreover, the recent ruling by the US Supreme Court that genes are not patentable has opened up the genetic testing field, at least in the USA, in an unprecedented manner.

Multiple Susceptibility Loci for Radiation-Induced Mammary Tumorigenesis in F2[Dahl S x R]-Intercross Rats

Although two major breast cancer susceptibility genes, BRCA1 and BRCA2, have been identified accounting for 20% of breast cancer genetic risk, identification of other susceptibility genes accounting for 80% risk remains a challenge due to the complex, multi-factorial nature of breast cancer. Complexity derives from multiple genetic determinants, permutations of gene-environment interactions, along with presumptive low-penetrance of breast cancer predisposing genes, and genetic heterogeneity of human populations. As with other complex diseases, dissection of genetic determinants in animal models provides key insight since genetic heterogeneity and environmental factors can be experimentally controlled, thus facilitating the detection of quantitative trait loci (QTL). We therefore, performed the first genome-wide scan for loci contributing to radiation-induced mammary tumorigenesis in female F2-(Dahl S x R)-intercross rats. Tumorigenesis was measured as tumor burden index (TBI) after induction of rat mammary tumors at forty days of age via 127Cs-radiation. We observed a spectrum of tumor latency, size-progression, and pathology from poorly differentiated ductal adenocarcinoma to fibroadenoma, indicating major effects of gene-environment interactions. We identified two mammary tumorigenesis susceptibility quantitative trait loci (Mts-QTLs) with significant linkage: Mts-1 on chromosome-9 (LOD-2.98) and Mts-2 on chromosome-1 (LOD-2.61), as well as two Mts-QTLs with suggestive linkage: Mts-3 on chromosome-5 (LOD-1.93) and Mts-4 on chromosome-18 (LOD-1.54). Interestingly, Chr9-Mts-1, Chr5-Mts-3 and Chr18-Mts-4 QTLs are unique to irradiation-induced mammary tumorigenesis, while Chr1-Mts-2 QTL overlaps with a mammary cancer susceptibility QTL (Mcs 3) reported for 7,12-dimethylbenz-[α]antracene (DMBA)-induced mammary tumorigenesis in F2[COP x Wistar-Furth]-intercross rats. Altogether, our results suggest at least three distinct susceptibility QTLs for irradiation-induced mammary tumorigenesis not detected in genetic studies of chemically-induced and hormone-induced mammary tumorigenesis. While more study is needed to identify the specific Mts-gene variants, elucidation of specific variant(s) could establish causal gene pathways involved in mammary tumorigenesis in humans, and hence novel pathways for therapy.

In Brief: BRCA1 and BRCA2

The discovery of the first major breast cancer susceptibility gene, BRCA1, occurred almost 20 years ago. BRCA1, together with BRCA2 remain the most important discoveries in human cancer genetics. Identification of highly penetrant mutations in these two tumour suppressor genes has had broad implications for women at risk and their families, for health professionals caring for these persons and for basic researchers. The BRCA proteins have many critical functions, the most notable of which, from a clinical perspective, is repair of double-strand DNA breaks.

Is multiple SNP testing in BRCA2 and BRCA1 female carriers ready for use in clinical practice? Results from a large Genetic Centre in the UK.

BRCA1 and BRCA2 are major breast cancer susceptibility genes. Nineteen single nucleotide polymorphisms (SNPs) at 18 loci have been associated with breast cancer. We aimed to determine whether these predict breast cancer incidence in women with BRCA1/BRCA2 mutations. BRCA1/2 mutation carriers identified through the Manchester genetics centre between 1996 and 2011 were included. Using published odds ratios (OR) and risk allele frequencies, we calculated an overall breast cancer risk SNP score (OBRS) for each woman. The relationship between OBRS and age at breast cancer onset was investigated using the Cox proportional hazards model, and predictive ability assessed using Harrell's C concordance statistic. In BRCA1 mutation carriers we found no association between OBRS and age at breast cancer onset: OR for the lowest risk quintile compared to the highest was 1.20 (95% CI 0.82-1.75, Harrell's C = 0.54), but in BRCA2 mutation carriers the association was significant (OR for the lowest risk quintile relative to the highest was 0.47 (95% CI 0.33-0.69, Harrell's C = 0.59). The 18 validated breast cancer SNPs differentiate breast cancer risks between women with BRCA2 mutations, but not BRCA1. It may now be appropriate to use these SNPs to help women with BRCA2 mutations make maximally informed decisions about management options.

CHEK2 mutations as markers for high risk of breast cancer

Genetic testing for the two major breast cancer susceptibility genes, BRCA1 and BRCA2 is widely available in North America and Europe. A few other highly-penetrant breast cancer genes have been found, including p53, BRIP1 and PALB2, but families with mutations in these are exceedingly rare. Arguably, the most relevant of the post-BRCA genes, from a clinical point of view, is CHEK2, which was first linked to breast cancer susceptibility in 2002. In Poland, there are four founder mutations of CHEK2. Three of these (IVS2+1G>A, del5395 and 1100delC) are protein-truncating mutations and one (I157T) is a missense variant. We estimated the lifetime risk of breast cancer for carriers of CHEK2 truncating mutations to be 20% for a woman with no affected relative, 28% for a woman with one second-degree-relative affected, 34% for a woman with one first-degree relative affected, and 44% for a woman with both first- and one-second degree relative affected in the Polish population. In addition we estimated that the lifetime risk for breast cancer for women who carried two different CHEK2 mutations (a truncating mutation and the missense mutation) to be 42%. Our results confirm that CHEK2 mutation screening detects a clinically meaningful risk of breast cancer, and women with a truncating mutation in CHEK2 and a positive family history of breast cancer, and women who carry two different CHEK2 mutations (the missense mutation I157T and a truncating mutation) face a lifetime risk of breast cancer above 25% and are candidates for MRI screening and for tamoxifen chemoprevention.

BRCA1 and BRCA2: different roles in a common pathway of genome protection

The proteins encoded by the two major breast cancer susceptibility genes, BRCA1 and BRCA2, work in a common pathway of genome protection. However, the two proteins work at different stages in the DNA damage response (DDR) and in DNA repair. BRCA1 is a pleiotropic DDR protein that functions in both checkpoint activation and DNA repair, whereas BRCA2 is a mediator of the core mechanism of homologous recombination. The links between the two proteins are not well understood, but they must exist to explain the marked similarity of human cancer susceptibility that arises with germline mutations in these genes. As discussed here, the proteins work in concert to protect the genome from double-strand DNA damage during DNA replication.

A deleterious BRCA1 mutation in a young Pakistani woman with metaplastic breast carcinoma

Metaplastic breast carcinoma (MBC) is a relatively rare subtype of breast cancer that encompasses a pathologically heterogeneous group of tumors. Pathogenic germ line mutations in the major breast cancer susceptibility genes BRCA1 and BRCA2 genes have been rarely found or described in MBC. We report the identification of the BRCA1 185delAG mutation in a 22-year-old Pakistani woman with triple-negative MBC that showed biphasic morphological features, including sarcomatous and malignant epithelial components. A comprehensive description of the clinical, histopathological, morphological, and immunohistochemical features of the tumor and the patient's treatment course is presented.

A One-Step Prescreening for Point Mutations and Large Rearrangement in BRCA1 and BRCA2 Genes Using Quantitative Polymerase Chain Reaction and High-Resolution Melting Curve Analysis

High-resolution melting (HRM) of DNA is a versatile method for mutation scanning that monitors the fluorescence of double-strand DNA with saturating dye. Performing HRM on a real-time thermocycler enables semiquantitative analysis (quantitative polymerase chain reaction, qPCR) to be associated to HRM analysis for detection of both large gene rearrangements and point mutations (qPCR-HRM). We evaluated this method of mutation screening for the two major breast and ovarian cancer susceptibility genes BRCA1 and BRCA2. Screening of these two genes is time-consuming and must include exploration of large rearrangements that represent 5% to 15% of the alterations observed in these genes. To assess the reliability of the HRM technology, 201 known nucleotide variations scattered over all amplicons were tested. The sensitivity of qPCR was evaluated by analyzing seven large rearrangements. All previously identified variants tested were detected by qPCR-HRM. A retrospective study was done with 45 patients: qPCR-HRM allowed all the variants previously tested by denaturing high-performance liquid chromatography to be identified. qPCR analysis showed three cases of allele dropout (due to a 104-bp deletion, SNP primer mismatch, and an Alu insertion). A prospective study was done with 165 patients allowing 22 deleterious mutations, 16 unclassified variants, and 2 rearrangements to be detected. qPCR-HRM is a simple, sensitive, and fast method that does not require modified PCR primers. Thus, this method allows in one step the detection of point mutation, gene rearrangements, and prevention of missing a mutation due to primer mismatch.

Abstract LB-102: The p21Cip1/Waf1 cyclin-dependent kinase inhibitor is required for the activation of the FA-BRCA pathway

Abstract Fanconi anemia (FA) is a rare recessive disorder characterized in part by pronounced cancer susceptibility. The FA proteins, and the protein products of the major breast cancer susceptibility genes BRCA1 and BRCA2, function cooperatively in the FA-BRCA pathway, to repair damaged DNA and to prevent cellular transformation. A major step in the activation of the FA-BRCA pathway is the mono-ubiquitination of the FANCD2 and FANCI proteins, targeting these proteins to discrete chromatin-associated nuclear foci. Importantly, the regulation of FANCD2 (and FANCI) mono-ubiquitination remains poorly understood. To gain further insight into this important post-translational modification step, here we have examined the roles of p53 tumor suppressor as well its downstream target p21Cip1/Waf1 in the regulation of the mono-ubiquitination of FANCD2. In this study we have used the isogenic HCT116 p53+/+, p53−/−, p21+/+, and p21−/− cell lines, to determine that p21, and not p53, plays a key role in the regulation of the mono-ubiquitination of FANCD2 following exposure to DNA damaging agents. For example, robust FANCD2 mono-ubiquitination is observed in HCT116 p21+/+ cells 2 h following exposure to 20 J/m2 UV irradiation, while this effect is markedly attenuated in p21−/− cells. Using immunofluorescence microscopy we also demonstrate that p21 is necessary for the efficient recruitment of FANCD2 to nuclear foci following exposure to UV irradiation. Furthermore, preliminary protein-protein interaction analyses in COS-7 cells demonstrate that FLAG-p21 and 6xHis/V5-FANCD2 physically interact. Interestingly, despite a failure to efficiently activate the mono-ubiquitination of FANCD2 following exposure to DNA damaging agents, p21−/− cells are not hypersensitive to the cytotoxic effects of the DNA crosslinking agent mitomycin C (MMC). However, elevated levels of distinct chromosome aberrations, including telomere associations and dicentric chromosomes, are observed in p21−/− cells compared with p21+/+ cells following exposure to MMC. Taken together, our results demonstrate an important upstream role for the p21 cyclin-dependent-kinase inhibitor in the activation of the FA-BRCA pathway. A greater understanding of the regulation of this important tumor suppressor pathway will lead to improved diagnostic and therapeutic approaches to FA and enhance our understanding of the elevated cancer susceptibility of FA patients. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr LB-102.

Identification of personal risk of breast cancer: genetics

Family history has long been recognized to be a potent risk factor for breast cancer [1]. Family histories often comprise only one or two affected relatives, who frequently were not particularly young at onset. Occasionally, a family contains a striking constellation of young-onset breast (and often other) cancers apparently transmitted as a dominant genetic trait. Over a century ago, the much referenced French neurologist Paul Broca wrote about the family of his wife, in which the occurrence of many cancers, particularly of the breast, strongly suggested the presence of a genetic predisposition [1]. It was to be more than a hundred years before the discovery of the structure of DNA and rapid advances in molecular technology would allow the first major breast cancer susceptibility gene, BRCA1, to be mapped to chromosome 17q [2]. In families linked to the BRCA1 locus, a much younger age at onset than average and the frequent occurrence of ovarian cancers were noted to be typical. At about the same time, the cause of a rare but devastating familial cancer syndrome was identified; mutations in the TP53 gene had also been found to account for the very rare Li Fraumeni syndrome associated with very young onset breast cancers and childhood malignancy, particularly soft tissue sarcomas [3,4]. A second major breast cancer susceptibility gene, BRCA2, was mapped to chromosome 13q in 1994 shortly before the sequence of the BRCA1 gene was clarified and family-specific disease-causing mutations started to be reported [5,6]. The full BRCA2 gene sequence was reported in 1995 [7]. Families with mutations in the BRCA2 gene were noted to be more likely to contain a male breast cancer case than might be expected by chance (and more than had been seen in families due to BRCA1 mutations); ovarian and fallopian tube cancers still occurred with increased frequency but overall not as frequently as in BRCA1-associated families. With the discovery of the correct gene sequences for BRCA1 and BRCA2 it became possible to offer predictive genetic testing to members of families in which the causative gene mutation had been identified. Predictive testing for breast cancer susceptibility was introduced as a clinical service from the mid-1990s in some centres in the UK [8]. Families in which mutations were identified through research studies were the first to be informed [9]. Many of these families had been identified because of their high incidence of cancer, and so inevitably the estimated lifetime chance that a carrier of one of these genes would develop cancer was high [10,11]. The BRCA1 and BRCA2 genes are very large, and mutation testing was either very expensive (in the USA) or very slow (in European countries) when it first became available. It soon became clear that mutations in these genes accounted for a relatively small proportion of all families with breast cancer clusters. Families with four or more cancer cases developing at young age, particularly those families in which ovarian cancers occurred, were more likely to yield pathogenic mutations when DNA from a cancer-affected family member was screened for mutations. Smaller clusters of later onset cancers, although clearly familial, were noted to have a much lower probability of harbouring a BRCA1 or BRCA2 mutation [12]. In the presence of a BRCA1 or BRCA2 mutation, the lifetime risk for developing breast cancer may be as high as 80% to 90%, although other genes and lifestyle factors may reduce the lifetime risk to levels as low as 26%. Ovarian cancer risk in BRCA1 gene carriers is estimated at about 50%, but again this risk is likely to be modified by both genetic and other risk factors. For BRCA2, ovarian cancer risk is about 15%, but all these average risks are likely to be modified by context [13].

Novel BRCA2‐interacting protein BJ‐HCC‐20A inhibits the induction of apoptosis in response to DNA damage

The major hereditary breast cancer susceptibility gene BRCA2 is associated with familial breast and ovarian cancer. BRCA2 plays a role in DNA repair, transcription, cell cycle regulation, maintenance of genomic stability in response to DNA damage, centrosome regulation, and cytokinesis. To further understand the function of BRCA2, we used a yeast two-hybrid method and identified a novel BRCA2-interacting protein, BJ-HCC-20A, which is reported to be a potential cancer-testis antigen. We confirmed the interaction between endogenous BJ-HCC-20A and BRCA2 in mammalian cells, and showed that BJ-HCC-20A interacts with a portion of the highly conserved region of BRCA2 in various mammals, and M phase-specific phosphorylation of the binding region of BRCA2 modulates BJ-HCC-20A binding. Overexpression of BJ-HCC-20A increases cell growth, and downregulation of endogenous BJ-HCC-20A expression using small interfering RNA suppresses cell growth and leads to the induction of apoptosis. Importantly, the BJ-HCC-20A mRNA level is downregulated by adriamycin (ADR)-induced DNA damage and depletion of BJ-HCC-20A expression by small interfering RNA promotes the reduction of BRCA2 expression and enhances cell apoptosis in response to DNA damage. Additionally, the recovery of BJ-HCC-20A expression in ADR-induced DNA damage inhibits ADR-induced apoptosis. The data suggest that BJ-HCC-20A promotes cell growth and may regulate the induction of cell apoptosis in response to DNA damage in cooperation with BRCA2 in an M phase-dependent manner. Therefore, we speculate that targeting BJ-HCC-20A may aid in the treatment of breast tumors.

Use of association studies to define genetic modifiers of breast cancer risk in BRCA1 and BRCA2 mutation carriers

Though much progress has been made in understanding the role of two major high-risk breast cancer (BC) susceptibility genes, BRCA1 and BRCA2, it remains unclear what causes the observed variation in risk between mutation carriers. This marked variability in individual cancer risk both between and within BRCA1 and BRCA2 mutation carrier families may be partly explained by modifier genes that influence mutation penetrance. Defining these modifiers should help refine individual cancer risk estimates and is also expected to be an efficient method to identify further BC susceptibility alleles in general. This approach is predicated on the concept that variants in genes that are low to moderate penetrance predisposition genes are likely to have a larger risk modification effect in BRCA1/2 mutation carriers. Association studies are usually used to assess the influence of variants in biologically plausible candidate loci on the penetrance of BRCA1/2 mutations (i.e., differences in age of onset or tissue-specificity of disease). Several such modifier loci, including the genes AIB1 and AR involved in hormone metabolism, and the RAD51 gene acting in DNA repair, have been proposed in the literature. A consortium of laboratories (CIMBA) has recently confirmed the RAD51 135 G/C variant as a BC risk modifier in BRCA2 mutation carriers, though not in BRCA1 carriers. This review describes molecular epidemiological efforts to evaluate the potential influence of polymorphic variants in candidate modifier genes on the risk of BC conferred by the BRCA1 and BRCA2 genes.