The contribution of inherited factors to the clinicopathological features and behavior of breast cancer

This review is focused on genetic factors that may influence the development and/or appearance of breast cancer metastases. Over the last decade there have been significant advances in the understanding of genetic predisposition to breast cancer. The first breast cancer predisposing gene to be identified was TP53, and this was followed over the next 5 years by two more genes, BRCA1 and BRCA2, which from a population perspective are much more important than TP53. Other rarer genes have subsequently been identified, but the role of more common, less penetrant genes in breast cancer susceptibility remains unknown. Recent work has shown that breast cancers occurring in women carrying germ-line BRCA1 mutations tend to have clinicopathological features that are usually associated with a poor prognosis, such as high grade, estrogen receptor negative status and somatic TP53 mutations. On the other hand, they are usually ERBB2 negative. Whether or not such tumors are more or less likely to metastasize, and hence be associated with a poor outcome, is currently uncertain and has been the subject of much debate. Here, we outline some of the clinicopathological features of hereditary breast cancer, discuss the prognostic studies that have been performed, and introduce some possible new research directions.     

From BRCA1 to Polygenic Risk Scores: Mutation-Associated Risks in Breast Cancer-Related Genes

BackgroundThere has been huge progress over the last 30 years in identifying the familial component of breast cancer.SummaryCurrently around 20% is explained by the high-risk genes BRCA1 and BRCA2, a further 2% by other high-penetrance genes, and around 5% by the moderate risk genes ATM and CHEK2. In contrast, the more than 300 low-penetrance single-nucleotide polymorphisms (SNP) now account for around 28% and they are predicted to account for most of the remaining 45% yet to be found. Even for high-risk genes which confer a 40–90% risk of breast cancer, these SNP can substantially affect the level of breast cancer risk. Indeed, the strength of family history and hormonal and reproductive factors is very important in assessing risk even for a BRCA carrier. The risks of contralateral breast cancer are also affected by SNP as well as by the presence of high or moderate risk genes. Genetic testing using gene panels is now commonplace.Key-MessagesThere is a need for a more parsimonious approach to panels only testing those genes with a definite 2-fold increased risk and only testing those genes with challenging management implications, such as CDH1 and TP53, when there is strong clinical indication to do so. Testing of SNP alongside genes is likely to provide a more accurate risk assessment.     

Analysis of the gene coding for the BRCA2-interacting protein PALB2 in hereditary prostate cancer

BACKGROUND: The genetic basis of susceptibility to prostate cancer (PRCA) remains elusive. Mutations in BRCA2 have been associated with increased prostate cancer risk and account for around 2% of young onset (<56 years) prostate cancer cases. PALB2 is a recently identified breast cancer susceptibility gene whose protein is closely associated with BRCA2 and is essential for BRCA2 anchorage to nuclear structures. This functional relationship made PALB2 a candidate PRCA susceptibility gene. METHODS: We sequenced PALB2 in probands from 95 PRCA families, 77 of which had two or more cases of early onset PRCA (age at diagnosis <55 years), and the remaining 18 had one case of early onset PRCA and five or more total cases of PRCA. RESULTS: Two previously unreported variants, K18R and V925L were identified, neither of which is in a known PALB2 functional domain and both of which are unlikely to be pathogenic. No truncating mutations were identified. CONCLUSIONS: These results indicate that deleterious PALB2 mutations are unlikely to play a significant role in hereditary prostate cancer.     

The role of BRCA1 and BRCA2 in prostate cancer

One of the strongest risk factors for prostate cancer is a family history of the disease. Germline mutations in the breast cancer predisposition gene 2 (BRCA2) are the genetic events known to date that confer the highest risk of prostate cancer (8.6-fold in men ≤65 years). Although the role of BRCA2 and BRCA1 in prostate tumorigenesis remains unrevealed, deleterious mutations in both genes have been associated with more aggressive disease and poor clinical outcomes. The increasing incidence of prostate cancer worldwide supports the need for new methods to predict outcome and identify patients with potentially lethal forms of the disease. As we present here, BRCA germline mutations, mainly in the BRCA2 gene, are one of those predictive factors. We will also discuss the implications of these mutations in the management of prostate cancer and hypothesize on the potential for the development of strategies for sporadic cases with similar characteristics.     

Practical aspects of genetic counseling in breast cancer: Lights and shadows

In unselected populations, less than 10% of breast cancers are associated with germline mutations in predisposing genes. Breast cancer type 1 and 2 (BRCA1 and BRCA2) susceptibility genes are the most common involved genes and confer a 10–30 times higher risk of developing the disease compared to the general population. A personal or family history suggestive of inherited breast cancer syndrome may be further evaluated to assess the risk of genetic predisposition and the presence of a genetic mutation. Breast cancer genetic counseling should include a careful risk assessment with associated psychosocial evaluation and support, possible molecular testing, personalized discussion of results. Knowledge of BRCA status can influence individualized cancer risk-reduction strategies. i.e. active surveillance, prophylactic surgery and/or pharmacoprevention.     

Awareness and attitudes concerning BRCA gene testing

Background: The availability of a commercial test for the breast cancer susceptibility genes, BRCA1 and BRCA2, has generated interest in both the medical community and the general public. Methods: Patients and family members were approached in the waiting room and asked to fill out an anonymous questionnaire about their awareness of breast cancer genes and breast cancer gene testing, and their desire to be tested. ² analysis was used to analyze frequencies between groups. Results: A total of 354 women completed a questionnaire concerning the breast cancer genes BRCA1 and BRCA2. The very young, the very old, and African-Americans were the least informed in terms of awareness of the genes and the availability of testing for the breast cancer susceptibility genes. Jewish people, people with a college education or beyond, people earning more than $30,000 a year, and Caucasians were more aware of the genes and of testing for these genes. Interest in being tested was similar in all groups, except for participants over 60 and those who had only an elementary-school education. Conclusions: Information concerning the breast cancer susceptibility genes has not reached the general public uniformly. A concerted effort is needed if this information is to be passed on to those people at risk.Poster presented at the 50th Annual Cancer Symposium of The Society of Surgical Oncology, Chicago, Illinois, March 17–21, 1997.     

BRCA mutation characteristics in a series of index cases of breast cancer selected independent of family history

Certain genetic predisposition factors, such as BRCA1 and BRCA2 mutations play a pivotal role in familial breast cancer development in both males and females. Due to this, the importance and necessity of genetic screening to identify mutations affecting the population is paramount. Undergoing genetic screenings allows for a more knowledgeable risk assessment for the patients and their care providers. The aim of this study was to evaluate the prevalence of BRCA1/BRCA2 mutated genes in the Turkish population among unselected patients. To identify the molecular markers, we utilized a gene panel analysis consisting of BRCA1 and BRCA2 genes, with a next generation sequencing platform (MiSeq System, Illumina). Sequencing was performed using leukocyte DNA from breast cancer patients. In‐silico analysis for novel mutations was carried out using SIFT, PolyPhen2 and MutationTaster. BRCA1 and BRCA2 pathogenic variants were identified in 18 of 129 (14%) patients among the study population; of those 18 patients, seven (39%) were found in the BRCA1 gene and 11 (61%) in the BRCA2 gene. Ten of the eleven BRCA2 variants (90%) were novel mutations. Four of ten (40%) of the novel mutations were determined to be deleterious and six out of ten (60%) were identified as single nucleotide variations. Clinically significant mutations of the BRCA1/BRCA2 genes are related to an increased susceptibility for breast cancer. There is however, little known about BRCA mutations amongst the general population. Thus, it is important that patients are able to undergo genetic screenings and counseling. This also allows for greater care from health care providers and can only facilitate disease prevention which in turn can lead to a decreased cancer morbidity rate.     

ATM and Genome Maintenance: Defining Its Role in Breast Cancer Susceptibility

The ATM gene is mutated in ataxia-telangiectasia (A-T), a genetic instability syndrome characterized by increased cancer risk, as well as other features. Recent studies have shown that the ATM protein kinase plays a critical role in maintaining genome integrity by activating a biochemical chain reaction that in turn leads to cell cycle checkpoint activation and repair of DNA damage. ATM targets include well-known tumor suppressor genes such as p53 and BRCA1, both of which play an important role in predisposition to breast cancer. Studies of A-T families have consistently reported an increased risk of breast cancer in women with one mutated ATM gene, but so far an increased frequency of ATM mutations has not been found in women with breast cancer. Some specific missense and protein truncating variants of ATM have been reported to confer increased breast cancer risk, but the magnitude of this risk remains uncertain. A more comprehensive analysis of ATM is needed in large case-control studies, and in multiple-case breast cancer families.     

Inherited Mutations in Breast Cancer Genes—Risk and Response

Germ-line mutations in BRCA1 and BRCA2 confer a high risk of developing breast cancer. They account, however, for only 40% of strongly familial breast cancer cases. Intensive genome-wide searches for other highly-penetrant BRCA genes that, individually account for a sizeable fraction of the remaining heritability has not identified any plausible candidates. The “missing heritability” is thought to be due to cumulative effects of susceptibility alleles associated with low to moderate penetrance, in accordance with a polygenic model of inheritance. In addition, a large number of individually very rare, highly penetrant variants could account for part of the gap. Meanwhile, an understanding of the function of BRCA1 and BRCA2 in the DNA damage response pathway has lead to the identification of a number of breast cancer susceptibility genes including PALB2, CHEK2, ATM and BRIP1, all of which interact directly or indirectly with BRCA1 or BRCA2. Knowledge of how BRCA1 and BRCA2 maintain genomic integrity has also led the development of novel targeted therapies. Here we summarize the recent advances made in the understanding of the functions of these two genes, as well as the risks and responses associated with mutations in these and other breast cancer susceptibility genes.     

Expression of BRCA1 and BRCA2 in Normal and Neoplastic Cells

Current evidence strongly supports a role forthe breast cancer susceptibility genes, BRCA1 and BRCA2, in both normal development and carcinogenesis.Valuable clues regarding the function of these genes have been garnered through studies of theirpatterns of expression. A central feature of the in vivopattern of BRCA1 and BRCA2 expression is that each ofthese putative tumor suppressor genes is expressed at maximal levels in rapidly proliferatingcells. This feature is consistent with in vitroobservations that BRCA1 and BRCA2 are expressed in acell cycle-dependent manner. This feature is also wellillustrated during mammary gland development wherein theexpression of BRCA1 and BRCA2 is induced in rapidlyproliferating cellular compartments undergoingdifferentiation, such as terminal end buds duringpuberty and developing alveoli during pregnancy.Strikingly, the spatial and temporal patterns of BRCA1and BRCA2 expression are virtually indistinguishableduring embryonic development and in multiple adulttissues despite the fact that these genes areunrelated. These observations have contributed to theemerging hypothesis that these genes function in similarregulatory pathways.     

Genotype–Phenotype Correlations by Ethnicity and Mutation Location in BRCA Mutation Carriers

The genotype–phenotype correlations of the specific BRCA1 and BRCA2 mutations in multi‐ethnic populations in USA have not yet been fully investigated. This study was designed to evaluate the effects of ethnicity at specific mutation locations and breast/ovarian cancer phenotypes. Our cohort included 445 women with different ethnic backgrounds who underwent BRCA genetic testing between 1997 and 2010. Known clinical and pathologic characteristics were compared with Chi‐Square Analysis or Fisher's Exact test as appropriate. The three most common mutation locations in BRCA1 (exons 2, 11, and 20) and BRCA2 (exons 10, 11, and 25) genes were chosen. Prevalence of BRCA1 exon 2 mutations were significantly higher in Ashkenazi Jewish (AJ) women compared to Caucasians (41% versus 15%; p = 0.001). Similarly, AJ women with breast cancer were more likely to have BRCA1 exon 2 mutation (47% positivity in AJ women versus 0–12.5% positivity in other ethnicities; p = 0.004). Women carrying the exon 20 BRCA1 mutation had the highest probability of having combined breast and ovarian cancers compared to women carrying other exon mutations (p = 0.05). The median age at initial cancer diagnosis, phenotypic features of breast cancer tumors, and overall survival did not vary significantly by ethnicity or mutation location. Our data suggest that ethnicity does not affect age of onset, overall survival or confer different risks of breast and ovarian cancer development in BRCA carriers. These results also suggest that women carrying the exon 20 BRCA1 mutation may warrant mutation‐specific counseling and be more aggressively managed for risk reduction.     

Assessing the Knowledge and Attitudes Regarding Genetic Testing for Breast Cancer Risk in our Region of Southeastern Georgia

Abstract: Genetic testing for the breast cancer susceptibility genes, BRCA1 and BRCA2, has been available for over a decade. Positive test results carry significant medical, psychological, and social implications. Knowledge of the public’s awareness concerning BRCA testing, and perceived benefits and barriers to testing can help refine educational programs and identify subgroups needing additional support. Patients and their acquaintances with a breast complaint attending a surgical clinic or private office were asked to complete a questionnaire about their knowledge of breast cancer genes and their desire to be tested. Demographic information collected included ethnicity, education background, age, income, and personal and family history of breast cancer, knowledge of BRCA genes and testing, and their willingness to participate in genetic counseling. A total of 222 people completed the questionnaire that showed the majority of subjects in southeast Georgia believe breast cancer is inherited 26–50% of the time. Caucasians and those with advanced degrees are the most informed regarding awareness of BRCA genes (p < 0.05); the least informed groups include African Americans and those with no more than a college education. Participants with a family history of breast cancer were significantly more likely to know that genes had been identified that indicate an increased risk of breast cancer (p < 0.05). A history of breast cancer did not impact the degree of awareness (p > 0.05). Subjects aware of genetic testing are more willing to utilize counseling (p < 0.05). Perceptions of breast cancer inheritance, awareness of susceptibility genes, and availability of testing and counseling are not uniform among all population subgroups. In southeast Georgia, educational efforts should focus on the less educated and minority groups.     

Personalized prevention in high risk individuals: Managing hormones and beyond

Increasing numbers of women are being identified at ‘high-risk’ of breast cancer, defined by The National Institute of Health and Care Excellence (NICE) as a 10-year risk of ≥8%. Classically women have been so identified through family history based risk algorithms or genetic testing of high-risk genes. Recent research has shown that assessment of mammographic density and single nucleotide polymorphisms (SNPs), when combined with established risk factors, trebles the number of women reaching the high risk threshold. The options for risk reduction in such women include endocrine chemoprevention with the selective estrogen receptor modulators tamoxifen and raloxifene or the aromatase inhibitors anastrozole or exemestane. NICE recommends offering anastrozole to postmenopausal women at high-risk of breast cancer as cost effectiveness analysis showed this to be cost saving to the National Health Service. Overall uptake to chemoprevention has been disappointingly low but this may improve with the improved efficacy of aromatase inhibitors, particularly the lack of toxicity to the endometrium and thrombogenic risks. Novel approaches to chemoprevention under investigation include lower dose and topical tamoxifen, denosumab, anti-progestins and metformin.Although oophorectomy is usually only recommended to women at increased risk of ovarian cancer it has been shown in numerous studies to reduce breast cancer risks in the general population and in those with mutations in BRCA1/2. However, recent evidence from studies that have confined analysis to true prospective follow up have cast doubt on the efficacy of oophorectomy to reduce breast cancer risk in BRCA1 mutation carriers, at least in the short-term.     

Heterogenic Loss of the Wild-Type BRCA Allele in Human Breast Tumorigenesis

Background For individuals genetically predisposed to breast and ovarian cancer through inheritance of a mutant BRCA allele, somatic loss of heterozygosity affecting the wild-type allele is considered obligatory for cancer initiation and/or progression. However, several lines of evidence suggest that phenotypic effects may result from BRCA haploinsufficiency. Methods Archival fixed and embedded tissue specimens from women with germ line deleterious mutations in BRCA1 or BRCA2 were identified. After pathologic review, focal areas of normal breast epithelium, atypical ductal hyperplasia, ductal carcinoma-in-situ, and invasive ductal carcinoma were identified from 14 BRCA1-linked and 9 BRCA2-linked breast cancers. Ten BRCA-linked prophylactic mastectomy specimens and 12 BRCA-linked invasive ovarian carcinomas were also studied. Laser catapult microdissection was used to isolate cells from the various pathologic lesions and corresponding normal tissues. After DNA isolation, real-time polymerase chain reaction assays were used to quantitate the proportion of wild-type to mutant BRCA alleles in each tissue sample. Results Quantitative allelotyping of microdissected cells revealed a high level of heterogeneity in loss of heterozygosity within and between preinvasive lesions and invasive cancers from BRCA1 and BRCA2 heterozygotes with breast cancer. In contrast, all BRCA-associated ovarian cancers displayed complete loss of the wild-type BRCA allele. Conclusions These data suggest that loss of the wild-type BRCA allele is not required for BRCA-linked breast tumorigenesis, which would have important implications for the genetic mechanism of BRCA tumor suppression and for the clinical management of this patient population.     

Developmental Studies of Brca1 and Brca2 Knock-Out Mice

In humans, the inheritance of mutations in thebreast cancer susceptibility genes BRCA1 and BRCA2increases the risk of developing breast and ovariancancer. To study their biological function and to create animal models for these cancer susceptibilitygenes, several strains of mice mutated in the homologousgenes Brca1 and Brca2 have been generated by genetargeting. Analyses of these knock-out mouse mutants have provided invaluableknowledge about the function of these genes. Brca1 andBrca2 null mutants are similar in phenotype: mutationsin both genes result in embryonic lethality and thedeveloping embryos show signs of a cellular proliferationdefect associated with activation of the p53 pathway.The significance of this activation, as well as the roleof these cancer susceptibility genes in DNA damage repair, is discussed.     

Alcohol consumption and the risk of breast cancer among BRCA1 and BRCA2 mutation carriers

Alcohol consumption increases the risk of breast cancer among women in the general population, but its effect on women who carry a BRCA gene mutation is unclear. We conducted a case-control study of 1925 matched pairs of predominantly premenopausal women who carry a BRCA1 or a BRCA2 mutation. Information on current alcohol consumption was obtained from a questionnaire administered during the course of genetic counselling or at the time of enrolment. A modest inverse association between breast cancer and reported current alcohol consumption was observed among women with a BRCA1 mutation (OR = 0.82, 95% CI 0.70–0.96), but not among women with a BRCA2 mutation (OR = 1.00; 95% CI 0.71–1.41). Compared to non-drinkers, exclusive consumption of wine was associated with a significant reduction in the risk of breast cancer among BRCA1 carriers (p-trend = 0.01). Alcohol consumption does not appear to increase breast cancer risk in women carrying a BRCA gene mutation.     

Prophylaktische Chirurgie des Mamma- und Ovarialkarzinoms

New insights into the genetic basis of carcinogenesis have been obtained by modern molecular biological techniques. Several susceptibility genes are known. The hereditary breast and ovarian cancer syndrome (germline mutations in BRCA1 and BRCA2) and endometrial cancer in the context of the hereditary non-polyposis colorectal cancer syndrome (HNPCC), germline mutations in mismatch-repair genes, are the most frequent hereditary cancer syndromes in gynaecology. Mutations in TP53 (Li-Fraumeni syndrome) and PTEN (Cowden's disease), associated with increased risk of breast cancer, are responsible for a smaller portion of familial breast cancer.The risk of inheritance and disease can be identified and defined by investigating family history, risk calculation programs, and genetic testing. Afterwards, options of primary, secondary, and tertiary prevention can be formulated. Presently, prophylactic surgery is the only option proven by clinical trials that can reduce the mortality of hereditary breast and ovarian cancer.     

Functional Domains of the BRCA1 and BRCA2 Proteins

The BRCA1 and BRCA2 genes encode large unrelatedproteins that presumably function as tumor suppressorsin normal epithelial cells of the breast. However, theprimary amino acid sequences of these proteins provide few insights into the mechanisms bywhich BRCA1 and BRCA2 inhibit tumor development.Nevertheless, recent studies have uncovered manysimilarities in the biological properties of BRCA1 andBRCA2, raising the prospect that these proteins mayfunction in a common pathway of tumor suppression andthat inactivation of either gene may represent anequivalent step in the development of breast cancer. Several lines of evidence now suggest a rolefor BRCA1 and BRCA2 in the cellular response to DNAdamage, possibly by virtue of their relationship withproteins required for the recombinational repair of double-strand DNA breaks. Accordingly, the lossof BRCA1 or BRCA2 function might accelerate tumordevelopment by allowing cells to accumulate DNA lesionsthat are potentially oncogenic.     

Glutathione S-transferase polymorphisms associated with risk of breast cancer in southern Taiwan

In this study, the genetic polymorphisms associated with breast cancer in southern Taiwan were investigated. Two categories of genes were analyzed: (1) BRCA1, BRCA2, and Rad51, the DNA repair factors involved in homologous recombinational repair; and (2) CYP1A1, COMT, GST, and NAT2, the xenobiotic-metabolizing enzymes (XME) involved in estrogen metabolism. We found that the number of deletions and/or mutations in the GST genes was highly correlated with the occurrence of breast cancer. These data suggest that the GST enzymes, which detoxify the catechol estrogen quinones, are important target molecules for screening in populations at high risk of breast cancer.     

Moderate penetrance genes complicate genetic testing for breast cancer diagnosis: ATM,CHEK2, BARD1 and RAD51D

Breast cancer risk associated with germline likely pathogenic/pathogenic variants (PV) varies by gene, often by penetrance (high >50% or moderate 20–50%), and specific locus.Germline PVs in BRCA1 and BRCA2 play important roles in the development of breast and ovarian cancer in particular, as well as in other cancers such as pancreatic and prostate cancers and melanoma. Recent studies suggest that other cancer susceptibility genes, including ATM, CHEK2, PALB2, RAD51C and RAD51D confer differential risks of breast and other specific cancers.In the era of multigene panel testing, advances in next-generation sequencing technologies have notably reduced costs in the United States (US) and enabled sequencing of BRCA1/2 concomitantly with additional genes. The use of multigene-panel testing is beginning to expand in Europe as well.Further research into the clinical implications of variants in moderate penetrance genes, particularly in unaffected carriers, is needed for appropriate counselling and risk management with data-driven plans for surveillance and/or risk reduction. For individuals at high risk without any pathogenic or likely pathogenic variant in cancer susceptibility genes or some carriers of pathogenic variants in moderate-risk genes such as ATM and CHEK2, polygenic risk scores offer promise to help stratify breast cancer risk and guide appropriate risk management options.Cancer patients whose tumours are driven by the loss of function of both copies of a predisposition gene may benefit from therapies targeting the biological alterations induced by the dysfunctional gene e.g. poly ADP ribose polymerase (PARP) inhibitors and other novel pathway agents in cancers with DNA repair deficiencies. A better understanding of mechanisms by which germline variants drive various malignancies may lead to improvements in both therapeutic and preventive management options.