Partner And Localizer Of BRCA2 Mutations Research Articles

Development and validation of molecular methodologies to assess PALB2 expression in sporadic breast cancer

ObjectivesRecent reports have included PALB2 (Partner and localizer of BRCA2) in the growing list of hereditary cancer genes. PALB2 mutations confer a moderate breast cancer risk in heterozygotes and Fanconi anemia in biallelic mutation carriers. PALB2 protein co-localizes with BRCA2 and BRCA1 in nuclear structures and enables error-free homologous recombination repair of double-stranded DNA breaks. This important contribution could be severely diminished if affected by epigenetic mechanisms such as promoter CpG island methylation. The aim of our study was to develop molecular methodologies in order to assess accurately PALB2 expression in breast cancer tissues. Design and methodsDNA and RNA were extracted from 91 sporadic fresh-frozen breast tissues with known histopathological data. DNA was subjected to sodium bisulfite conversion reaction and the CpG island of the PALB2 promoter was analyzed by pyrosequencing. RNA was converted to cDNA and analyzed by a newly developed and validated RT-qPCR assay based on a hydrolysis probe (TaqMan) in the Light Cycler. ResultsPALB2 promoter was not methylated in any of the samples tested. 87 out of 91 (95.6%) primary tumors were positive for PALB2 expression, as checked at the mRNA level. When levels of PALB2 mRNA were compared to histopathological data (tumor size, grade, lymph node involvement, metastasis, hormone receptors and HER2 overexpression), no significant statistical correlation was found. ConclusionsDNA methylation is an unlike mechanism for PALB2 transcriptional regulation. PALB2 mRNA expression does not seem be a promising prognostic biomarker for sporadic breast cancer.

Analysis of PALB2 mutations in 155 Japanese patients with breast and/or ovarian cancer.

PALB2 (Partner and Localizer of BRCA2) was identified as a moderate-risk gene in breast and pancreatic cancers. Recently, it was reported that PALB2 carriers have a high risk of developing breast cancer, with the cumulative risk of 34 % by the age of 70. Peripheral blood samples from 155 patients at risk for hereditary breast and/or ovarian cancer were tested for BRCA1/2 and PALB2 by targeted sequencing using a next-generation sequencer. Of these 155, 146 met NCCN criteria and the remaining 9 did not. BRCA1/2 analysis was performed on 155 patients, for whom the results were reported previously (Hirotsu Y et al. Mol Genet Genomic Med, doi:10.1002/mgg3.157, 2015). Eleven patients were identified to have deleterious BRCA mutations (Hirotsu Y et al. Mol Genet Genomic Med, doi:10.1002/mgg3.157, 2015). However, none of the 155 patients were found to have deleterious PALB2 germline mutations. Missense mutations [variants of uncertain significance (VUS)] of PALB2 were found in 12 cases. In silico analyses by SIFT (Sorting Intolerant Form Tolerant) and PolyPhen2 (Polymorphism Phenotyping version 2) indicated that 2 of 12 VUS were deleterious and probably damaging. This is the first report on PALB2 mutations in Japan, revealing two missense mutations as "deleterious and probably damaging" by in silico analyses, but no PALB2 premature truncation mutations were identified. The sample size is relatively small and a larger cohort study is needed in Japan.

Abstract P4-12-16: Teasing out the PALB2 phenotype

Abstract Background: Biallelic mutations in PALB2 (Partner and Localizer of BRCA2) are known to cause Fanconi Anemia Type N. Multiple reports have demonstrated an increased risk for cancer in individuals heterozygous for PALB2 mutations. For example, a recent study by Antoniou et al reported a 33-58% lifetime risk for breast cancer in PALB2 mutation carriers, with 30% of carriers reporting triple negative breast cancer (TNBC). Other studies have suggested associations between PALB2 heterozygosity and pancreatic cancer, ovarian cancer, male breast cancer, and prostate cancer as well. We aimed to better define PALB2 phenotypes by assessing clinical history of TNBC, pancreatic, ovarian, and prostate cancers amongst PALB2 mutation carriers identified via multigene panel testing. Methods: We reviewed clinical histories of 11,007 individuals who underwent PALB2 sequence and deletion/duplication analysis as part of a multigene hereditary cancer panel. Descriptive statistics were utilized for clinical histories of PALB2 carriers, and chi square analysis was used to compare clinical histories of PALB2 mutation carriers to mutation-negative controls. Individuals with mutations in other cancer susceptibility genes were excluded from analysis. Results: A total of 98 PALB2 mutation carriers identified among 9610 individuals were included in our analysis. The majority of mutation carriers were Caucasian (80%) and female (92.8%). All identified mutations were truncating (nonsense, frameshift, or gross deletions). No pathogenic missense mutations were identified in this cohort. 77.6% (n=76) of mutation carriers had breast cancer, diagnosed at a mean age of 48. Hormone receptor status was available for 48 mutation carriers and 2469 controls. 37.5% (18/48) of breast cancers in mutation carriers were reported as triple negative, compared to 17.1% (423/2469) of breast cancers in controls (OR: 2.9 ; p= 0.0002). 7.8% (n= 8) of PALB2 mutation carriers had ovarian cancer. There was no significant difference in the incidence of ovarian cancer between PALB2 mutation carriers and controls (OR: 0.65 ; p= 0.25). Additionally, mutation carriers were significantly less likely to have a family history of ovarian cancer than controls (OR: 0.5; p= 0.02). 5.9% (n=6) of mutation carriers had pancreatic cancer, diagnosed at a mean age of 57.8, compared to 61 for controls. PALB2 mutation carriers were 1.3 times more likely to have personal and/or family history of pancreatic cancer, although this was not statistically significant (p= 0.22). Similarly, PALB2 mutation carriers were 1.5 times more likely to have a family history of prostate cancer, although this was not statistically significant (p= 0.09). Conclusions: Our data supports existing literature associating PALB2 mutations with TNBC. We did not observe significant associations between PALB2 carrier status and a clinical history of pancreatic, prostate, or ovarian cancers. However, this data should be interpreted with caution, as it is possible that unidentified genetic factors contributed to the clinical history of cancer in our mutation-negative controls. Investigation of PALB2-associated cancer risks in an unselected prospective cohort would help to further elucidate the PALB2 phenotype. Citation Format: Emily K Dalton, Rachel McFarland, Holly Laduca, Shuwei Li, Chia-Ling Gau. Teasing out the PALB2 phenotype [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P4-12-16.

Two PALB2 germline mutations found in both BRCA1+ and BRCAx familial breast cancer.

Partner and localizer of BRCA2 (PALB2), plays an important functional role in DNA damage repair. Recent studies indicate that germline mutations in PALB2 predispose individuals to a high risk of developing familial breast cancer. Therefore, comprehensive identification of PALB2 germline mutations is potentially important for understanding their roles in tumorigenesis and for testing their potential utility as clinical targets. Most of the previous studies of PALB2 have focused on familial breast cancer cases with normal/wild-type BRCA1 and BRCA2 (BRCAx). We hypothesize that PALB2 genetic mutations also exist in individuals with BRCA mutations (BRCA+). To test this hypothesis, PALB2 germline mutations were screened in 107 exome data sets collected from familial breast cancer families who were either BRCA1+ or BRCAx. Two novel heterozygous mutations predicted to alter the function of PALB2 were identified (c.2014G>C, p.E672Q and c.2993G>A, p.G998E). Notably, both of these mutations co-existed in BRCA1+ and BRCA1x families. These studies show that mutations in PALB2 can occur independent of the status of BRCA1 mutations, and they highlight the importance to include BRCA1+ families in PALB2 mutation screens.

Partner and Localizer of BRCA-2 (PALB-2) Mutation Analysis Is Rapidly Being Adopted into Clinical Practice.

To the Editor, Breast-Cancer Risk in Families with Mutations in PALB2: A.C. Antoniou, S. Casadei, T. Heikkinen, et al. N Engl J Med. 2014;371:497-506. In a study published in N Engl J Med. August 2014, researchers from 14 centers in eight countries investigated information from 362 family members from 154 families who had an abnormal partner and localizer of BRCA2 (PALB2) gene, but did not have an abnormal BRCA1 or BRCA2 gene. Their aim was to demonstrate the importance of loss-of-function mutations in PALB2 as a cause of hereditary breast cancer. The study included 311 women with an abnormal PALB2 gene; 229 of these women had been diagnosed with breast cancer and 51 men with an abnormal PALB2 gene; seven of whom had been diagnosed with breast cancer. The researchers compared the breast cancer risk of the study population to the general population. They found out that overall, women with an abnormal PALB2 gene had a risk of breast cancer that was 9.47 times higher than average. Women with an abnormal PALB2 gene had a 14% risk of developing breast cancer by age 50 and a 35% risk of developing breast cancer by age 70. The average lifetime risk of breast cancer is about 12%. This increase in risk linked to an abnormal PALB2 gene was dependent on the women’s age and family history. They have demonstrated that the relative risk of breast cancer among PALB2 mutation carriers increased significantly as birth cohort became more recent (P<0.001). In women with an abnormal PALB2 gene, breast cancer risk was eight to nine times higher than average in women aged 20 to 39, six to eight times higher than average in women aged 40 to 60, and five times higher than average in women older than 60 years of age. By the age of 70, women with an abnormal PALB2 gene with no family history of breast cancer had a 33% risk of developing breast cancer whereas women with two or more first-degree relatives with breast cancer at 50 years of age had a 58% risk of developing the disease. The authors concluded that based on their estimates, breast cancer risk for a PALB2 mutation carrier, even in the absence of a family history of breast cancer, would be classified as high according to various guidelines. The researchers also reported that this level of risk may justify adding PALB2 to genetic testing for BRCA1 and BRCA2. A Genetic counselor’s perspective Partner and localizer of BRCA2 (PALB) is a gene whose protein facilitates the function of BRCA2 and interacts with BRCA1 to aid in repairing double strand and interstrand cross-link DNA damage. Biallelic PALB2 mutations cause Fanconi Anemia complement group N (FANCN) and monoallellic mutations in the PALB2 gene are associated with increased breast and pancreas cancer risks (1). PALB2 mutations may account for as much as 3% of familial breast cancer risk (2). A recent study of 362 members from PALB2 mutation positive families found that the risk for breast cancer in female mutation carriers ranged between 33% to 58% by age 70, with the higher risks relating to those women with a family history of early onset (<50) breast cancer in 2 first degree family members (3). The study also identified an 8 fold increase in male breast cancer risk and a 2 fold increase in ovarian cancer risk, both of which need to be confirmed in additional studies due a lack of statistical significance. These data suggest that female PALB2 mutation carriers may have breast cancer risks that are similar to those conferred by mutations in the BRCA2 gene. These findings suggest that women who carry PALB2 gene mutations may warrant similar breast cancer screening and prevention strategies as those offered to BRCA2 mutation carriers. PALB2 mutation analysis is available and is rapidly being adopted into clinical practice. As the data continues to accumulate it is likely that PALB2 mutation analysis will become a standard part of genetic testing in the realm of hereditary breast cancer predisposition. Whether testing will be done in addition to BRCA1/2 or as part of a larger breast cancer gene panel remains to be determined. In addition, more data will provide evidence to support the development of specific management guidelines to aid in the care of these at risk patients.

Assessment of PALB2 as a candidate melanoma susceptibility gene.

Partner and localizer of BRCA2 (PALB2) interacts with BRCA2 to enable double strand break repair through homologous recombination. Similar to BRCA2, germline mutations in PALB2 have been shown to predispose to Fanconi anaemia as well as pancreatic and breast cancer. The PALB2/BRCA2 protein interaction, as well as the increased melanoma risk observed in families harbouring BRCA2 mutations, makes PALB2 a candidate for melanoma susceptibility. In order to assess PALB2 as a melanoma predisposition gene, we sequenced the entire protein-coding sequence of PALB2 in probands from 182 melanoma families lacking pathogenic mutations in known high penetrance melanoma susceptibility genes: CDKN2A, CDK4, and BAP1. In addition, we interrogated whole-genome and exome data from another 19 kindreds with a strong family history of melanoma for deleterious mutations in PALB2. Here we report a rare known deleterious PALB2 mutation (rs118203998) causing a premature truncation of the protein (p.Y1183X) in an individual who had developed four different cancer types, including melanoma. Three other family members affected with melanoma did not carry the variant. Overall our data do not support a case for PALB2 being associated with melanoma predisposition.

Detection of a large rearrangement in PALB2 in Spanish breast cancer families with male breast cancer

It has been demonstrated that monoallelic PALB2 (Partner and Localizer of BRCA2) gene mutations predispose to familial breast cancer. Some of the families reported with germline PALB2 mutations presented male breast cancer as a characteristic clinical feature. Therefore, we wanted to investigate the contribution of germline PALB2 mutations in a set of 131 Spanish BRCA1/BRCA2-negative breast/ovarian cancer families with at least one male breast cancer case. The analysis included direct sequencing of all coding exons and intron/exon boundaries as well as a Multiplex Ligation-dependent Probe Amplification-based analysis of genomic rearrangements. For the first time we have identified a genomic rearrangement of PALB2 gene involving a large deletion from exon 7 to 11 in a breast cancer family. We have also identified several PALB2 variants, but no other obvious deleterious PALB2 mutation has been found. Thus, our study does not support an enrichment of PALB2 germline mutations in the subset of breast cancer families with male breast cancer cases. The identification of intronic and exonic variants indicates the necessity of assessing the implications of variants that do not lead to PALB2 truncation in the pathoghenicity of the PALB2 gene.

PALB2 mutations in familial breast and pancreatic cancer

PALB2 (Partner And Localizer of BRCA2) binds to and co-localizes with BRCA2 in DNA repair. Germline mutations in PALB2 have been identified in approximately 1-2% of familial breast cancer and 3-4% of familial pancreatic cancer cases. The goal of this study was to evaluate the prevalence of PALB2 mutations in women with breast cancer without BRCA1/2 mutations who also had a personal or family history of pancreatic cancer. PALB2 mutation analysis was performed in 94 non-BRCA1/2 breast cancer patients with a personal or family history of pancreatic cancer. Two truncating PALB2 mutations, c.3549C>CA and c.2962C>CT, were identified resulting in a mutation prevalence of 2.1%. The proband found to carry the c.3549C>CA PALB2 mutation had a mother diagnosed with both breast and pancreatic cancer; this relative was subsequently confirmed to carry the identical mutation. The proband with the c.2962C>CT mutation had a father and paternal aunt diagnosed with pancreatic cancer; neither relative was available for testing. Two novel PALB2 missense variants were also found, one of which was deemed potentially deleterious. The prevalence rate of PALB2 mutations in a non-BRCA1/2 breast cancer population specifically selected for a family history of pancreatic cancer does not appear to be significantly increased compared to that observed in other breast cancer populations studied thus far. Further evaluation is needed to determine the prevalence of PALB2 mutations and the clinical utility of such testing in those individuals affected with both breast and pancreatic cancers.

Germline mutations in the PALB2 gene are population specific and occur with low frequencies in familial breast cancer

The Partner and Localizer of BRCA2 (PALB2) protein has been linked to Fanconi anemia and breast cancer predisposition. Here we present data of a comprehensive mutation screening of the PALB2 gene in 818 familial cases of breast cancer from Germany. By analyzing the entire coding region of PALB2, we found seven truncating mutations (six of them novel) in families tested negative for BRCA1/2-mutations. In addition, two novel potentially disease causing missense mutations were found. Remarkably, only one mutation reported previously in other populations, was also identified in the German population. No PALB2 mutation carriers were identified in 450 unaffected controls. Thus, our observations indicate a low prevalence of deleterious PALB2 mutations and a specific mutation profile within the German population. As PALB2-deficient tumors were shown to be sensitive to Poly(ADP-ribose) Polymerase (PARP) inhibitors, our study has implications for newly developed, favorable treatment options in familial breast cancer.

PALB2 mutations in German and Russian patients with bilateral breast cancer

Since germline mutations in the PALB2 (Partner and Localizer of BRCA2) gene have been identified as breast cancer (BC) susceptibility alleles, the geographical spread and risks associated with PALB2 mutations are subject of intense investigation. Patients with bilateral breast cancer constitute a valuable group for genetic studies. We have thus scanned the whole coding region of PALB2 in a total of 203 German or Russian bilateral breast cancer patients using an approach based on high-resolution melting analysis and direct sequencing of genomic DNA samples. Truncating PALB2 mutations were identified in 4/203 (2%) breast cancer patients with bilateral disease. The two nonsense mutations, p.E545X and p.Q921X, have not been previously described whereas the two other mutations, p.R414X and c.509_510delGA, are recurrent. Our results indicate that PALB2 germline mutations account for a small, but not negligible, proportion of bilateral breast carcinomas in German and Russian populations.Electronic supplementary materialThe online version of this article (doi:10.1007/s10549-010-1290-4) contains supplementary material, which is available to authorized users.

Structural basis for recruitment of BRCA2 by PALB2

The breast cancer 2, early onset protein (BRCA2) is central to the repair of DNA damage by homologous recombination. BRCA2 recruits the recombinase RAD51 to sites of damage, regulates its assembly into nucleoprotein filaments and thereby promotes homologous recombination. Localization of BRCA2 to nuclear foci requires its association with the partner and localizer of BRCA2 (PALB2), mutations in which are associated with cancer predisposition, as well as subtype N of Fanconi anaemia. We have determined the structure of the PALB2 carboxy-terminal beta-propeller domain in complex with a BRCA2 peptide. The structure shows the molecular determinants of this important protein-protein interaction and explains the effects of both cancer-associated truncating mutants in PALB2 and missense mutations in the amino-terminal region of BRCA2.

PALB2 sequence variants in young South African breast cancer patients

PALB2 (partner and localizer of BRCA2) is a recently identified breast cancer susceptibility gene, in which mutations confer doubling of breast cancer risk with moderate to low penetrance. Recent studies in various populations report that deleterious mutations in this gene account for approximately 1% of familial or early-onset breast cancer cases. This study aimed to determine the involvement of PALB2 mutations in a cohort of 48 young (29-45 years) South African breast cancer patients unselected for family history of breast cancer. The complete coding region and intron-exon boundaries of PALB2 were analyzed. A novel truncating mutation, c.697delG (V233fs) was identified in one patient. A missense variant (E211G), identified in another patient, appears to be segregating with the disease, but in silico analysis using SIFT, PolyPhen and A-GVGD, indicates that this variant is nonpathogenic. In addition, four other missense, one synonymous and three intronic variants were detected, all of which appear polymorphic. This represents the second study to analyze the role of PALB2 in early-onset breast cancer patients unselected for family history. The first study, of a Chinese population, established that PALB2 was responsible for 1.3% of early-onset breast cancer cases. Our study reports that deleterious mutations in PALB2 account for approximately 2% (1/48) of South African early-onset breast cancer.