BRCA1 and BRCA2 pathways and the risk of cancers other than breast or ovarian

OBJECTIVE: Germline mutations in the tumor suppressor genes BRCA1 and BRCA2 predispose women to breast and ovarian cancer. Female carriers of BRCA1 or BRCA2 gene mutations have very high lifetime risks for breast and ovarian cancers. Genetic abnormalities occur in all cancers, so BRCA-related pathways are critical because they serve to safeguard genetic content. Although protecting genetic information is a general function, BRCA-related pathways seem largely specific to preventing breast and ovarian cancer. The objective of this study was to resolve this difference between the theoretical functions of BRCA genes and their specific clinical effects. DATA SOURCES, DATA EXTRACTION, DATA SYNTHESIS: The author collected data published in > 30 epidemiologic studies on the incidence of cancers other than breast or ovarian in mutation carriers and in large populations eligible for mutation testing. Data were extracted and used directly as published whenever possible with a minimum of statistical manipulation. CONCLUSIONS: Although mutations target breast and ovary, a broader spectrum of cancers also occur with statistically significant elevated frequencies. Risks for "all cancers except breast or ovary" are elevated, with some population subgroups differing with regard to how frequently elevated risks were found at individual sites. Additional sites at risk included stomach, pancreas, prostate, and colon. The increased risk ranged from about 20% to 60%, with the greatest increases in risk in stomach and pancreas. The collected data show BRCA-pathway functions are probably required at multiple sites, not just in breast or ovary. Known interactions and relationships among BRCA-related pathways strongly support the idea that their inactivation provides growth or survival advantages for a variety of cancers. The data suggest applying an increased level of clinical alertness to those with defects in BRCA-related pathways. Identifying molecules that confer growth or survival advantages to BRCA-related cancers may provide broadly useful targets for chemotherapy or chemoprevention.     

Interplay among BRCA1, SIRT1, and Survivin during BRCA1-associated tumorigenesis

Germline mutations of BRCA1 predispose women to breast and ovarian cancers. However, the downstream mediators of BRCA1 function in tumor suppression remain elusive. We found that human BRCA1-associated breast cancers have lower levels of SIRT1 than their normal controls. We further demonstrated that mammary tumors from Brca1 mutant mice have low levels of Sirt1 and high levels of Survivin, which is reversed by induced expression of Brca1. BRCA1 binds to the SIRT1 promoter and increases SIRT1 expression, which in turn inhibits Survivin by changing the epigenetic modification of histone H3. Absence of SIRT1 blocks the regulation of Survivin by BRCA1. Furthermore, we demonstrated that activation of Sirt1 and inhibition of Survivin expression by resveratrol elicit a more profound inhibitory effect on Brca1 mutant cancer cells than on Brca1-wild-type cancer cells both in vitro and in vivo. These findings suggest that resveratrol treatment serves as an excellent strategy for targeted therapy for BRCA1-associated breast cancer.     

Characterization of common BRCA1 and BRCA2 variants

Many missense variants identified in BRCA1 and BRCA2, two genes responsible for the majority of hereditary breast and ovarian cancer, are of unclear clinical significance. Characterizing the significance of such variants is important for medical management of patients in whom they are identified. The aim of this study was to characterize eight of the most common reported missense mutations in BRCA1 and BRCA2 occurring in patients tested for hereditary risk of breast and ovarian cancers. The prevalence of each variant in a control population, co-segregation of the variant with cancer within families, location of the variant within the gene, the nature of the amino acid substitution and conservation of the wild-type amino acid among species were considered. In a control population, the BRCA1 variants M1652I, R1347G, and S1512I, were each observed at a frequency of 4.08%, 2.04%, and 2.04%, respectively, and the BRCA2 variants A2951T, V2728I, and D1420Y, were seen at 1.02%, 0.68%, and 0.34%, respectively. Although the BRCA2 variants T598A and R2034C were not seen in this group of controls, other clinical and published observations indicate that these variants are not deleterious. Based on epidemiological and biological criteria, we therefore conclude that the BRCA1 missense mutations R1347G, S1512I and M1652I, and the BRCA2 missense mutations T598A, D1420Y, R2034C, V2728I, and A2951T, are not deleterious mutations.     

Genetic heterogeneity in hereditary breast cancer: role of BRCA1 and BRCA2.

The common hereditary forms of breast cancer have been largely attributed to the inheritance of mutations in the BRCA1 or BRCA2 genes. However, it is not yet clear what proportion of hereditary breast cancer is explained by BRCA1 and BRCA2 or by some other unidentified susceptibility gene(s). We describe the proportion of hereditary breast cancer explained by BRCA1 or BRCA2 in a sample of North American hereditary breast cancers and assess the evidence for additional susceptibility genes that may confer hereditary breast or ovarian cancer risk. Twenty-three families were identified through two high-risk breast cancer research programs. Genetic analysis was undertaken to establish linkage between the breast or ovarian cancer cases and markers on chromosomes 17q (BRCA1) and 13q (BRCA2). Mutation analysis in the BRCA1 and BRCA2 genes was also undertaken in all families. The pattern of hereditary cancer in 14 (61%) of the 23 families studied was attributed to BRCA1 by a combination of linkage and mutation analyses. No families were attributed to BRCA2. Five families (22%) provided evidence against linkage to both BRCA1 and BRCA2. No BRCA1 or BRCA2 mutations were detected in these five families. The BRCA1 or BRCA2 status of four families (17%) could not be determined. BRCA1 and BRCA2 probably explain the majority of hereditary breast cancer that exists in the North American population. However, one or more additional genes may yet be found that explain some proportion of hereditary breast cancer.     

Prevalence and penetrance of germline BRCA1 and BRCA2 mutations in a population series of 649 women with ovarian cancer

A population-based series of 649 unselected incident cases of ovarian cancer diagnosed in Ontario, Canada, during 1995-96 was screened for germline mutations in BRCA1 and BRCA2. We specifically tested for 11 of the most commonly reported mutations in the two genes. Then, cases were assessed with the protein-truncation test (PTT) for exon 11 of BRCA1, with denaturing gradient gel electrophoresis for the remainder of BRCA1, and with PTT for exons 10 and 11 of BRCA2. No mutations were found in all 134 women with tumors of borderline histology. Among the 515 women with invasive cancers, we identified 60 mutations, 39 in BRCA1 and 21 in BRCA2. The total mutation frequency among women with invasive cancers, 11.7% (95% confidence interval [95%CI] 9.2%-14.8%), is higher than previous estimates. Hereditary ovarian cancers diagnosed at age <50 years were mostly (83%) due to BRCA1, whereas the majority (60%) of those diagnosed at age >60 years were due to BRCA2. Mutations were found in 19% of women reporting first-degree relatives with breast or ovarian cancer and in 6.5% of women with no affected first-degree relatives. Risks of ovarian, breast, and stomach cancers and leukemias/lymphomas were increased nine-, five-, six- and threefold, respectively, among first-degree relatives of cases carrying BRCA1 mutations, compared with relatives of noncarriers, and risk of colorectal cancer was increased threefold for relatives of cases carrying BRCA2 mutations. For carriers of BRCA1 mutations, the estimated penetrance by age 80 years was 36% for ovarian cancer and 68% for breast cancer. In breast-cancer risk for first-degree relatives, there was a strong trend according to mutation location along the coding sequence of BRCA1, with little evidence of increased risk for mutations in the 5' fifth, but 8.8-fold increased risk for mutations in the 3' fifth (95%CI 3.6-22.0), corresponding to a carrier penetrance of essentially 100%. Ovarian, colorectal, stomach, pancreatic, and prostate cancer occurred among first-degree relatives of carriers of BRCA2 mutations only when mutations were in the ovarian cancer-cluster region (OCCR) of exon 11, whereas an excess of breast cancer was seen when mutations were outside the OCCR. For cancers of all sites combined, the estimated penetrance of BRCA2 mutations was greater for males than for females, 53% versus 38%. Past studies may have underestimated the contribution of BRCA2 to ovarian cancer, because mutations in this gene cause predominantly late-onset cancer, and previous work has focused more on early-onset disease. If confirmed in future studies, the trend in breast-cancer penetrance, according to mutation location along the BRCA1 coding sequence, may have significant impact on treatment decisions for carriers of BRCA1-mutations. As well, BRCA2 mutations may prove to be a greater cause of cancer in male carriers than previously has been thought.     

Founder mutations in the BRCA1 gene in Polish families with breast-ovarian cancer

We have undertaken a hospital-based study, to identify possible BRCA1 and BRCA2 founder mutations in the Polish population. The study group consisted of 66 Polish families with cancer who have at least three related females affected with breast or ovarian cancer and who had cancer diagnosed, in at least one of the three affected females, at age <50 years. A total of 26 families had both breast and ovarian cancers, 4 families had ovarian cancers only, and 36 families had breast cancers only. Genomic DNA was prepared from the peripheral blood leukocytes of at least one affected woman from each family. The entire coding region of BRCA1 and BRCA2 was screened for the presence of germline mutations, by use of SSCP followed by direct sequencing of observed variants. Mutations were found in 35 (53%) of the 66 families studied. All but one of the mutations were detected within the BRCA1 gene. BRCA1 abnormalities were identified in all four families with ovarian cancer only, in 67% of 27 families with both breast and ovarian cancer, and in 34% of 35 families with breast cancer only. The single family with a BRCA2 mutation had the breast-ovarian cancer syndrome. Seven distinct mutations were identified; five of these occurred in two or more families. In total, recurrent mutations were found in 33 (94%) of the 35 families with detected mutations. Three BRCA1 abnormalities-5382insC, C61G, and 4153delA-accounted for 51%, 20%, and 11% of the identified mutations, respectively.     

Clinical significance of promoter hypermethylation of RASSF1A, RARbeta2, BRCA1 and HOXA5 in breast cancers of Indian patients

Promoter hypermethylation of genes is implicated in the pathogenesis of many cancers, including breast cancer. Herein, we analyzed the promoter methylation status of a panel of critical growth regulatory genes, RASSF1A, RARbeta2, BRCA1 and HOXA5, in 54 breast cancers and 5 distant normal breast tissues of Indian patients. The methylation data were correlated with clinicopathological characteristics and hormone receptor status to determine the impact of methylation in breast carcinogenesis. Promoter hypermethylation of RASSF1A was observed in 39/54 (72%), HOXA5 in 36/54 (67%), BRCA1 in 15/54 (28%) and RARbeta2 in 8/54 (15%) breast cancers. Our most significant findings were the association of RASSF1A methylation with nodal metastasis (p=0.05); and RARbeta2 methylation with age (all tumors in patients in the older age group were methylated, p=0.04). Further, the interactions between DNA methylation and hormone receptor biology in breast cancer cells are beginning to be clearly understood. In this context the association of HOXA5 methylation with loss of ERalpha (p=0.009) is noteworthy.     

The predictive value of BRCA1 and BRCA2 mutation testing

Genetic testing for mutations in BRCA1 and BRCA2, two genes predisposing to breast and ovarian cancers, is available to women with a relevant family history. The aim of this study was to estimate the positive and negative predictive value of clinical sequence analysis of these genes. A reference graph showing positive and negative predictive values over a range of pre-test risk was derived, taking into account the sensitivity and specificity of a full-sequence analysis test. High positive and negative predictive values were found for women with pre-test risk between 4% and 40%, a range of risk commonly seen in clinical testing. The predictive value of full sequence and single-site analysis of BRCA1 and BRCA2, therefore, compares favorably with other diagnostic medical tests. Our results provide a numerical estimate of the predictive value of BRCA testing, and as such, provide a valuable tool to healthcare providers and families as they interpret BRCA1 and BRCA2 test results.     

Total-genome analysis of BRCA1/2-related invasive carcinomas of the breast identifies tumor stroma as potential landscaper for neoplastic initiation

We have shown that the tumor microenvironment of sporadic breast cancer is diverse in genetic alterations and contributes to the cancer phenotype. The dynamic morphology of the mammary gland might be of special interest in hereditary breast/ovarian cancer syndrome (HBOC). We hypothesized that hotspots of loss of heterozygosity or allelic imbalance (LOH/AI) within the tumor stroma of BRCA1/2-related breast cancers provide an impaired mammary stroma that could facilitate later malignant transformation of the breast epithelium. We conducted a total genome LOH/AI scan of DNA derived from the epithelium and stroma of 51 BRCA1/2-related breast cancers, using 372 microsatellite markers. We compared these data with those from a set of 134 sporadic breast cancers. HBOC-related breast cancers accumulated significantly more genetic alterations than did sporadic breast cancers. BRCA1/2-related breast cancer stroma showed LOH/AI at 59.7% of all loci analyzed, similar to the average frequency of LOH/AI observed in the epithelium (66.2%). This is remarkably different from sporadic breast cancers, for which the average epithelial LOH/AI frequency (36.7%) far exceeds the average stromal LOH/AI frequency (28.4%) (P=.03). We identified 11 hotspot loci of LOH/AI in the BRCA1/2 stroma, encompassing genes such as POLD1, which functions in DNA replication, and SDHB. In a subset of samples, enriched for BRCA1 cases, we found 45.0% overall LOH/AI in the stroma, which was significantly higher than the 41.8% LOH/AI observed in corresponding epithelium (P=.04). Together, our data indicate that, in HBOC-related breast cancers, the accumulation of genomic instability in the cancer stroma coincides with that in the neoplastic epithelium, and we postulate that such a genetically unstable stroma might facilitate a microenvironment that functions as a landscaper that promotes genomic instability in the epithelium and, subsequently, neoplastic transformation.     

Genomic rearrangements in BRCA1 and BRCA2: A literature review

Women with mutations in the breast cancer genes BRCA1 or BRCA2 have an increased lifetime risk of developing breast, ovarian and other BRCA-associated cancers. However, the number of detected germline mutations in families with hereditary breast and ovarian cancer (HBOC) syndrome is lower than expected based upon genetic linkage data. Undetected deleterious mutations in the BRCA genes in some high-risk families are due to the presence of intragenic rearrangements such as deletions, duplications or insertions that span whole exons. This article reviews the molecular aspects of BRCA1 and BRCA2 rearrangements and their frequency among different populations. An overview of the techniques used to screen for large rearrangements in BRCA1 and BRCA2 is also presented. The detection of rearrangements in BRCA genes, especially BRCA1, offers a promising outlook for mutation screening in clinical practice, particularly in HBOC families that test negative for a germline mutation assessed by traditional methods.     

The Basal Phenotype of BRCA1-Related Breast Cancer: Past,Present and Future

Many BRCA1-related tumors have a distinct histological characteristics which together have been called “basal-like”. Typically such tumors are ER-, HER2- and express cytokeratin 5/6, cytokeratin 8/18, EGFR and vimentin. These characteristics can be used to predict which breast cancers are most likely to be associated with germline BRCA1 mutations which has important implications for breast pathologists. Moreover, BRCA1-related breast cancers generally have a poorer prognosis which may paradoxically be more pronounced in node negative cancers. This may relate in part to a different pattern of metastatic spread with in increased frequency of brain and lung metastases in BRCA1 carriers. Conversely, BRCA1-related tumors may respond better to neoadjuvant chemotherapy and their characteristic molecular signature may provide opportunities to develop specific molecular targeted therapies akin to traztuzumab in HER2+ cancers. Finally, many of the phenotypic features of BRCA1-related tumors might also be found in putative breast stem cells and therefore characterization of the BRCA1 breast cancer phenotype will improve our understanding of sporadic breast carcinogenesis.     

BRCA1-directed,enhanced and aberrant homologous recombination

Despite intense studies, questions still remain regarding the molecular mechanisms leading to the development of hereditary breast and ovarian cancers. Research focused on elucidating the role of the breast cancer susceptibility gene 1 (BRCA1) in the DNA damage response may be of the most critical importance to understanding these processes. The BRCA1 protein has an N-terminal RING domain possessing E3 ubiquitinligase activity and a C-terminal BRCT domain involved in binding specific phosphoproteins. These domains are involved directly or indirectly in DNA double-strand break (DSB) repair. As the two terminal domains of BRCA1 represent two separate entities, understanding how these domains communicate and are functionally altered in regards to DSB repair is critical for understanding the development of BRCA1-related breast and ovarian cancers and for developing novel therapeutics. Herein, we review recent findings of how altered functions of these domains might lead to cancer through a mechanism of increased aberrant homologous recombination and possible implications for the development of BRCA1 inhibitors.     

Evaluation of the needs of male carriers of mutations in BRCA1 or BRCA2 who have undergone genetic counseling

To date, the concerns of men at risk of inheriting a BRCA1 mutation or a BRCA2 mutation have received little attention. It had been anticipated that few men would be interested in predictive testing when a BRCA mutation was identified in their family. However, these men are often affected emotionally by diagnoses of breast cancer in their relatives and may themselves harbor fears that cancer will develop. Male carriers of BRCA1/2 mutations are at increased risk of development of cancers of several types, including those of the breast and prostate. We conducted an evaluation of the needs and experiences of 59 male carriers of BRCA1/2 mutations followed at either the University of Toronto or Creighton University. We assessed their motivations for seeking genetic counseling and testing, involvement in family discussions of breast and ovarian cancer, risk perception, changes in cancer-screening practices, and overall satisfaction with the genetic-counseling process. The principal motivation for seeking genetic counseling was concern for their daughters. The majority (88%) of men participated in family conversations about breast and ovarian cancer, and 47% participated in conversations about prophylactic surgery. Most men believed that they were at increased risk of development of cancer (prostate, breast, colorectal, and skin cancers). However, fewer than one-half (43%) of the men with no previous diagnosis of cancer stated that their prostate cancer-surveillance practices had changed after they had received genetic test results. More than one-half (55%) had intrusive thoughts about their cancer risk. Although levels of satisfaction were high, practitioners should be aware of (a) potential pressures influencing men to request predictive testing, (b) the difficulties that men encounter in establishing surveillance regimens for breast and prostate cancer, and (c) the general lack of information about men's particular experiences in the medical community.     

Management updates for women with a BRCA1 or BRCA2 mutation

In most cases of families with breast and ovarian cancer, the pattern of cancers in the family can be attributed to mutations in the BRCA1 and BRCA2 genes. Genetic testing for these cancer susceptibility genes typically takes place in the context of comprehensive genetic counseling. Strategies have been developed for the medical management of women at high risk of developing breast cancer, including options for screening and prophylactic surgery. BRCA1 and BRCA2 carriers are recommended to undergo prophylactic bilateral salpingo-oophorectomy by age 35-40 years or when childbearing is complete. This surgery significantly reduces the risk of ovarian cancer and also reduces the risk of breast cancer when performed in premenopausal mutation carriers. For breast cancer management, BRCA1 and BRCA2 carriers are offered the options of increased surveillance, with or without chemoprevention, or prophylactic surgery. Currently, BRCA carrier status is not used as an independent prognostic factor regarding systemic treatment options.     

BRCA1 and stem cells: tumour typecasting

Phenotypic variation between tumour types is likely to reflect the nature of the cell of origin and the genes involved in pathogenesis. Compared with most sporadic breast cancers, those arising in carriers of BRCA1 mutations usually have distinctive pathological characteristics. A new study suggests that a role for BRCA1 in the determination of stem-cell fate may explain this phenomenon.     

First BRCA1 and BRCA2 gene testing implemented in the health care system of Stockholm

The aim of the study was to optimize the criteria for the BRCA1 and BRCA2 gene testing and to improve oncogenetic counseling in the Stockholm region. Screening for inherited breast cancer genes is laborious and a majority of tested samples turn out to be negative. The frequencies of mutations in the BRCA1 and BRCA2 genes differ across populations. Between 1997 and 2000, 160 families with breast and/or ovarian cancer were counseled and screened for mutations in the two genes. Twenty-five BRCA1 and two BRCA2 disease-causing mutations were found. Various factors associated with the probability of finding a BRCA1 mutation in the families were estimated. Age of onset in different generations and other malignancies were also studied. Families from our region in which both breast and ovarian cancer occur were likely to carry a BRCA1 mutation (34%). In breast-only cancer families, mutations were found only in those with very early onset. All breast- only cancer families with a mutation had at least one case of onset before 36 years of age and a young median age of onset (<43 years). Other malignancies than breast and ovarian cancers did not segregate in the BRCA1 families and surveillance for other malignancies is not needed, in general. Decreasing age of onset with successive generations was common and must be taken into account when surveillance options are considered.     

BRCA2 in American families with four or more cases of breast or ovarian cancer: recurrent and novel mutations, variable expression, penetrance, and the possibility of families whose cancer is not attributable to BRCA1 or BRCA2.

In order to evaluate the role of inherited BRCA2 mutations in American families--particularly the appearance in America of European founder mutations--the BRCA2 coding sequence, 5' UTR, and 3' UTR were screened in 22 Caucasian American kindreds with four or more cases of breast or ovarian cancer. Six mutations were found that cause a premature-termination codon; four of them have been reported elsewhere, and two are novel. In the four families with previously seen mutations, the distinct lineages at high risk of cancer were of Dutch, German, Irish, and Ashkenazi Jewish ancestry; mutations in Europe reflect these ancestries. The families with novel mutations were Puerto Rican Hispanic (exon 9 deletion 995delCAAAT) and Ashkenazi Jewish (exon 11 deletion 6425delTT). Among female BRCA2-mutation carriers, risks of breast cancer were 32% by age 50 years, 67% by age 70 years, and 80% by age 90 years, yielding a lifetime risk similar to that for BRCA1 but an older distribution of ages at onset. BRCA2 families also included multiple cases of cancers of the male breast (six cases), ovary (three cases), fallopian tube (two cases), pancreas (three cases), bladder (two cases), and prostate (two cases). Among 17 Ashkenazi Jewish families with four or more breast or ovarian cancers, 9 families (including 3 with ovarian cancer and 1 with male breast cancer) carried none of the three ancient mutations in BRCA1 or BRCA2. To date, both BRCA2 and BRCA1 have been screened by SSCA, supplemented by the protein-truncation test, in 48 families with four or more breast or ovarian cancers. Mutations have been detected in BRCA1 in 33 families, in BRCA2 in 6 families, and in neither gene in 9 families, suggesting both the probable cryptic nature of some mutations and the likelihood of at least one other BRCA gene.