Analysis of PALB2/FANCN-associated breast cancer families

Novel germline PALB2 truncating mutations in African American breast cancer patients

BACKGROUND

It has been demonstrated that the partner and localizer of breast cancer 2 (PALB2) acts as a bridging molecule between the breast cancer 1 (BRCA1) and BRCA2 proteins and is responsible for facilitating BRCA2-mediated DNA repair. Truncating mutations in the PALB2 gene reportedly are enriched in patients with Fanconi anemia and breast cancer in various populations.

METHODS

The authors evaluated the contribution of PALB2 germline mutations in 279 African American women with breast cancer, including 29 patients with a strong family history, 29 patients with a moderate family history, 75 patients with a weak family history, and 146 patients with nonfamilial or sporadic breast cancer.

RESULTS

After direct sequencing of all the coding exons, exon/intron boundaries, and 5' and 3' untranslated regions of PALB2, 3 novel, monoallelic, truncating mutations (1.08%; 3 in 279 patients) were identified (c.758dupT [exon 4], c.1479delC [exon 4], and c.3048delT [exon 10]) together with 50 sequence variants, 27 of which were novel. None of the truncating mutations were identified in a group of 262 controls from the same population.

CONCLUSIONS

PALB2 mutations were present in both familial and nonfamilial breast cancers among African Americans. Rare PALB2 mutations accounted for a small but substantial proportion of patients with breast cancer.

Unraveling the mechanism of BRCA2 in homologous recombination

BRCA2 is the product of a breast cancer susceptibility gene in humans and the founding member of an emerging family of proteins present throughout the eukaryotic domain that serve in homologous recombination. The function of BRCA2 in recombination is to control RAD51, a protein that catalyzes homologous pairing and DNA strand exchange. By physically interacting with both RAD51 and single-stranded DNA, BRCA2 mediates delivery of RAD51 preferentially to sites of single-stranded DNA (ssDNA) exposed as a result of DNA damage or replication problems. Through its action, BRCA2 helps restore and maintain integrity of the genome. This review highlights recent studies on BRCA2 and its orthologs that have begun to illuminate the molecular mechanisms by which these proteins control homologous recombination.

Using mouse models to investigate the biological and physiological consequences of defects in the Fanconi anaemia/breast cancer DNA repair signalling pathway

Fanconi anaemia (FA) is a rare, predominantly autosomal recessive syndrome (with one X-linked form) that results in congenital defects, abnormal haematopoiesis and a greatly increased risk of solid tumours in humans. Mutations in at least 14 different genes have been shown to cause FA, and several of these genes, including FANCJ/BRIP1, FANCD1/BRCA2 and FANCN/PALB2, also predispose to breast cancer in heterozygote carriers. The FA genes code for proteins that act in complexes to coordinate the repair of damaged DNA, and thus the FA repair network is intimately linked with hereditary breast cancer. Much remains to be learnt about the functions and interactions of the FA proteins and one experimental approach involves the generation of mice that are deficient in various FA genes. Mouse models for FANCN/PALB2 have recently been generated, including one reported in a recent issue of The Journal of Pathology. Given the pivotal role of the PALB2 protein, which interacts with both BRCA1 and BRCA2, these mice provide valuable insights into the FA phenotype and mechanisms of tumourigenesis caused by disruption of the FA protein network.

Mutations in BRCA2 and PALB2 in male breast cancer cases from the United States

Male breast cancer (MBC) is an uncommon disease with a frequency of approximately one in 1000. Due to the rarity of MBC, it is understudied and its etiology is poorly understood. Our objectives are to determine the frequency of pathogenic mutations in BRCA2 and PALB2 in MBC cases and to investigate the correlations between mutation status and cancer phenotypes. Single strand conformation polymorphism analysis, direct sequencing, and multiplex ligation-dependent probe amplification were employed to screen for mutations in the BRCA2 gene, followed by direct sequencing of the PALB2 gene in BRCA2-negative MBC cases. Pathogenic BRCA2 mutations were identified in 18 of the 115 MBC cases, including four of the ten cases (40%) from breast cancer families and 14 of the 105 cases (13%) unselected for family history of breast cancer. The difference in BRCA2-mutation frequencies between cases with and without family history of breast cancer was not statistically significant (P = 0.145), suggesting that family history is not a strong predictor of carrying a mutation in males. We observed a highly significant association of carrying a pathogenic BRCA2 mutation with high tumor grade (P < 0.001) and a weak association with positive lymph nodes (P < 0.02). Of the 97 BRCA2-negative MBC cases, we identified one PALB2 mutation with confirmed pathogenicity and one mutation predicted to be pathogenic, a prevalence of pathogenic PALB2-mutation of 1-2%. Based on our results and previous studies, genetic testing for BRCA2 should be recommended for any diagnosed MBC case, regardless of family history of breast cancer.

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.

Phenotype-genotype correlation in familial breast cancer

Familial breast cancer accounts for a small but significant proportion of breast cancer cases worldwide. Identification of the candidate genes is always challenging specifically in patients with little or no family history. Therefore, a multidisciplinary team is required for the proper detection and further management of these patients. Pathologists have played a pivotal role in the cataloguing of genotypic-phenotypic correlations in families with hereditary cancer syndromes. These efforts have led to the identification of histological and phenotypic characteristics that can help predict the presence or absence of germline mutations of specific cancer predisposition genes. However, the panoply of cancer phenotypes associated with mutations of genes other than in BRCA1 is yet to be fully characterised; in fact, many cancer syndromes, germline mutations and gene sequence variants are under investigation for their possible morphological associations. Here we review the current understanding of phenotype-genotype correlation in familial breast cancer.

BRIP1, PALB2, and RAD51C mutation analysis reveals their relative importance as genetic susceptibility factors for breast cancer

Mutations in the recognized breast cancer susceptibility genes BRCA1, BRCA2, TP53, ATM, and CHEK2 account for approximately 20% of hereditary breast cancer. This raises the possibility that mutations in other biologically relevant genes may be involved in genetic predisposition to breast cancer. In this study, BRIP1, PALB2, and RAD51C were sequenced for mutations as a result of previously being associated with breast cancer risk due to their role in the double-strand break repair pathway and their close association with BRCA1 and BRCA2. Two truncating mutations in PALB2 (Q66X and W1038X), one of which is has not been reported before, were detected in an independent Australian cohort of 70 individuals with breast or ovarian cancer, and have strong family histories of breast or breast/ovarian cancer. In addition, six missense variants predicted to be causative were detected, one in BRIP1 and five in PALB2. No causative variants were identified in RAD51C. This study supports recent observations that although rare, PALB2 mutations are present in a small but substantial proportion of inherited breast cancer cases, and indicates that RAD51C at a population level does not account for a substantial number of familial breast cancer cases.

Contribution of inherited mutations in the BRCA2-interacting protein PALB2 to familial breast cancer

Inherited mutations in the BRCA2-interacting protein PALB2 are known to be associated with increased risks of developing breast cancer. To evaluate the contribution of PALB2 to familial breast cancer in the United States, we sequenced the coding sequences and flanking regulatory regions of the gene from constitutional genomic DNA of 1,144 familial breast cancer patients with wild-type sequences at BRCA1 and BRCA2. Overall, 3.4% (33/972) of patients not selected by ancestry and 0% (0/172) of patients specifically of Ashkenazi Jewish ancestry were heterozygous for a nonsense, frameshift, or frameshift-associated splice mutation in PALB2. Mutations were detected in both male and female breast cancer patients. All mutations were individually rare: the 33 heterozygotes harbored 13 different mutations, 5 previously reported and 8 novel mutations. PALB2 heterozygotes were 4-fold more likely to have a male relative with breast cancer (P = 0.0003), 6-fold more likely to have a relative with pancreatic cancer (P = 0.002), and 1.3-fold more likely to have a relative with ovarian cancer (P = 0.18). Compared with their female relatives without mutations, increased risk of developing breast cancer for female PALB2 heterozygotes was 2.3-fold (95% CI: 1.5-4.2) by age 55 and 3.4-fold (95% CI: 2.4-5.9) by age 85. Loss of the wild-type PALB2 allele was observed in laser-dissected tumor specimens from heterozygous patients. Given this mutation prevalence and risk, consideration might be given to clinical testing of PALB2 by complete genomic sequencing for familial breast cancer patients with wild-type sequences at BRCA1 and BRCA2.

PALB2: a novel inactivating mutation in a Italian breast cancer family

Rare germline monoallelic mutations in PALB2 confer a relative risk of breast cancer of 2 to 4-times. To better define the role of PALB2 in breast cancer susceptibility in Italian breast or breast-ovarian cancer families we screened 95 index cases negative for BRCA1/BRCA2 germline mutations. The mutational analysis of the PALB2 gene in a index case of an high risk breast cancer family, has identified a frameshift mutation (c.1517delG) in the exon 4 that leads to the formation of a stop codon, 12 residues downstream of the mutation (Leu451X). The mutation was identified in a woman 52 year old with an infiltrating ductal breast carcinoma and in two of the three sisters without breast cancer. Our results confirmed that PALB2 could be a susceptibility gene for familial breast cancer also in Italian population.

Loss of p53 partially rescues embryonic development of Palb2 knockout mice but does not foster haploinsufficiency of Palb2 in tumour suppression

PALB2 interacts with BRCA1 and BRCA2 in supercomplexes involved in DNA repair via homologous recombination. Heterozygous germline mutations in PALB2 confer a moderate risk of breast cancer, while biallelic PALB2 mutations are linked to a severe form of Fanconi anaemia characterized by early childhood solid tumours and severe chromosomal instability. In contrast to BRCA1- or BRCA2-associated cancers, breast tumours in heterozygous PALB2 mutation carriers do not show loss of the wild-type allele, suggesting PALB2 might be haploinsufficient for tumour suppression. To study the role of PALB2 in development and tumourigenesis, we have generated Palb2(GT) mouse mutants using a gene trap approach. Whereas Palb2(GT/GT) homozygous mutant embryos died at mid-gestation due to massive apoptosis, Palb2(GT/+) heterozygous mice were viable and did not show any obvious abnormalities. Deletion of p53 alleviated the phenotype of Palb2(GT/GT) embryos, but did not rescue embryonic lethality. In addition, loss of p53 did not significantly collaborate with Palb2 heterozygosity in tumourigenesis in heterozygous or homozygous p53 knockout mice. Tumours arising in Palb2(GT/+) ;p53(+/-) or Palb2(GT/+) ;p53(-/-) compound mutant mice retained the wild-type Palb2 allele and did not display increased genomic instability.

Germline mutations in PALB2 in African-American breast cancer cases

Breast cancer incidence is lower in African Americans than in Caucasian Americans. However, African-American women have higher breast cancer mortality rates and tend to be diagnosed with earlier-onset disease. Identifying factors correlated to the racial/ethnic variation in the epidemiology of breast cancer may provide better understanding of the more aggressive disease at diagnosis. Truncating germline mutations in PALB2 have been identified in approximately 1% of early-onset and/or familial breast cancer cases. To date, PALB2 mutation testing has not been performed in African-American breast cancer cases. We screened for germline mutations in PALB2 in 139 African-American breast cases by denaturing high-performance liquid chromatography and direct sequencing. Twelve variants were identified in these cases and none caused truncation of the protein. Three missense variants, including two rare variants (P8L and T300I) and one common variant (P210L), were predicted to be pathogenic, and were located in a coiled-coil domain of PALB2 required for RAD51- and BRCA1-binding. We investigated and found no significant association between the P210L variant and breast cancer risk in a small case-control study of African-American women. This study adds to the literature that PALB2 mutations, although rare, appear to play a role in breast cancer in all populations investigated to date.

DICER1 mutations in familial multinodular goiter with and without ovarian Sertoli-Leydig cell tumors

CONTEXT

Nontoxic multinodular goiter (MNG) is frequently observed in the general population, but little is known about the underlying genetic susceptibility to this disease. Familial cases of MNG have been reported, and published reports describe 5 families that also contain at least 1 individual with a Sertoli-Leydig cell tumor of the ovary (SLCT). Germline mutations in DICER1, a gene that codes for an RNase III endoribonuclease, have been identified in families affected by pleuropulmonary blastoma (PPB), some of whom include cases of MNG and gonadal tumors such as SLCTs.

OBJECTIVE

To determine whether familial MNG with or without SLCT in the absence of PPB was associated with mutations in DICER1.

DESIGN, SETTING, AND PATIENTS

From September 2009 to September 2010, we screened 53 individuals from 2 MNG and 3 MNG/SLCT families at McGill University for mutations in DICER1. We investigated blood lymphocytes and MNG and SLCT tissue from family members for loss of the wild-type DICER1 allele (loss of heterozygosity), DICER1 expression, and microRNA (miRNA) dysregulation.

MAIN OUTCOME MEASURE

Detection of germline DICER1 gene mutations in familial MNG with and without SLCT.

RESULTS

We identified and characterized germline DICER1 mutations in 37 individuals from 5 families. Two mutations were predicted to be protein truncating, 2 resulted in in-frame deletions, and 1 was a missense mutation. Molecular analysis of the 3 SLCTs showed no loss of heterozygosity of DICER1, and immunohistochemical analysis in 2 samples showed strong expression of DICER1 in Sertoli cells but weak staining of Leydig cells. miRNA profiling of RNA from lymphoblastoid cell lines from both affected and unaffected members of the familial MNG cases revealed miRNA perturbations in DICER1 mutation carriers.

CONCLUSIONS

DICER1 mutations are associated with both familial MNG and MNG with SLCT, independent of PPB. These germline DICER1 mutations are associated with dysregulation of miRNA expression patterns.

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.

Cooperation of breast cancer proteins PALB2 and piccolo BRCA2 in stimulating homologous recombination

Inherited mutations in human PALB2 are associated with a predisposition to breast and pancreatic cancers. PALB2's tumor-suppressing effect is thought to be based on its ability to facilitate BRCA2's function in homologous recombination. However, the biochemical properties of PALB2 are unknown. Here we show that human PALB2 binds DNA, preferentially D-loop structures, and directly interacts with the RAD51 recombinase to stimulate strand invasion, a vital step of homologous recombination. This stimulation occurs through reinforcing biochemical mechanisms, as PALB2 alleviates inhibition by RPA and stabilizes the RAD51 filament. Moreover, PALB2 can function synergistically with a BRCA2 chimera (termed piccolo, or piBRCA2) to further promote strand invasion. Finally, we show that PALB2-deficient cells are sensitive to PARP inhibitors. Our studies provide the first biochemical insights into PALB2's function with piBRCA2 as a mediator of homologous recombination in DNA double-strand break repair.

PALB2/FANCN: recombining cancer and Fanconi anemia

Partner and localizer of BRCA2 (PALB2) was originally identified as a BRCA2-interacting protein that is crucial for key BRCA2 genome caretaker functions. It subsequently became clear that PALB2 was another Fanconi anemia (FA) gene (FANCN), and that monoallelic PALB2 mutations are associated with increased risk of breast and pancreatic cancer. Mutations in PALB2 have been identified in breast cancer families worldwide, and recent studies have shown that PALB2 also interacts with BRCA1. Here, we summarize the molecular functions and clinical phenotypes of this key DNA repair pathway component and discuss how its discovery has advanced our knowledge of both FA and adult cancer predisposition.

Role of homologous recombination in DNA interstrand crosslink repair

Homologous recombination repair (HRR) encompasses mechanisms that employ homologous DNA sequences as templates for repair or tolerance of a wide range of DNA lesions that inhibit DNA replication in S phase. Arguably the most imposing of these DNA lesions is that of the interstrand crosslink (ICL), consisting of a covalently attached chemical bridge between opposing DNA strands. ICL repair requires the coordinated activities of HRR and a number of proteins from other DNA repair and damage response systems, including nucleotide excision repair, base excision repair, mismatch repair, and translesion DNA synthesis (TLS). Interestingly, different organisms favor alternative methods of HRR in the ICL repair process. E. coli perform ICL repair using a homology-driven damage bypass mechanism analogous to daughter strand gap repair. Eukaryotes from yeast to humans initiate ICL repair primarily during DNA replication, relying on HRR activity to restart broken replication forks associated with double-strand break intermediates induced by nucleolytic activities of other excision repair factors. Higher eukaryotes also employ several additional factors, including members of the Fanconi anemia damage-response network, which further promote replication-associated ICL repair through the activation and coordination of various DNA excision repair, TLS, and HRR proteins. This review focuses on the proteins and general mechanisms of HRR associated with ICL repair in different model organisms.

PALB2 analysis in BRCA2-like families

BRCA2 and PALB2 function together in the Fanconi anemia (FA)-Breast Cancer (BRCA) pathway. Mono-allelic and bi-allelic BRCA2 and PALB2 mutation carriers share many clinical characteristics. Mono-allelic germline mutations of BRCA2 and PALB2 are risk alleles of female breast cancer and have also been reported in familial pancreatic cancer, and bi-allelic mutations cause a severe form of Fanconi anemia. In view of these similarities, we investigated whether the prevalence of PALB2 mutations was increased in breast cancer families with the occurrence of BRCA2 associated tumours other than female breast cancer. PALB2 mutation analysis was performed in 110 non-BRCA1/2 cancer patients: (a) 53 ovarian cancer patients from female breast-and/or ovarian cancer families; (b) 45 breast cancer patients with a first or second degree relative with pancreatic cancer; and (c) 12 male breast cancer patients from female breast cancer families. One truncating PALB2 mutation, c.509_510delGA, resulting in p.Arg170X, was found in a male breast cancer patient. We conclude that germline mutations of PALB2 do not significantly contribute to cancer risk in non-BRCA1/2 cancer families with at least one patient with ovarian cancer, male breast cancer, and/or pancreatic cancer.

Inactivation of Palb2 gene leads to mesoderm differentiation defect and early embryonic lethality in mice

Mutations of the PALB2 tumor suppressor gene in humans are associated with hereditary predisposition to breast and also some other cancers. In the present study, we have characterized mice deficient in Palb2. The data show that the Palb2((+/-)) mice are normal and fertile, and lack macroscopic tumors when followed up till the age of 8 months. Homozygous (HO) Palb2((-/-)) mice present with embryonic lethality and die at E9.5 at the latest. The mutant embryos are smaller in size, developmentally retarded and display defective mesoderm differentiation after gastrulation. In Palb2((-/-)) embryos, the expression of cyclin-dependent kinase inhibitor p21 is increased, and Palb2((-/-)) blastocysts show a growth defect in vitro. Hence, the phenotype of the Palb2((-/-)) mice in many regards resembles those previously reported for Brca1 and Brca2 knockout mice. The similarity in the phenotypes between Palb2, Brca1 and Brca2 knockout mice further supports the functional relationship shown in vitro for these three proteins. Accordingly, our data in vivo suggest that a key function for PALB2 is to interact with and to build up appropriate communication between BRCA1 and BRCA2, thereby licensing the successful performance of the physiological tasks mediated by these two proteins, particularly in homologous recombination and in proper DNA damage response signaling.

BRCA gene structure and function in tumor suppression: a repair-centric perspective

Germline mutations in the BRCA1 and BRCA2 genes are characterized by deficient repair of DNA double-strand breaks by homologous recombination. Defective DNA double-strand break repair has been not only implicated as a key contributor to tumorigenesis in mutation carriers but also represents a potential target for therapy. The transcriptional similarities between BRCA1-deficient tumors and sporadic tumors of the basal-like subtype have led to the investigation of homologous recombination repair-directed therapy in triple-negative tumors, which demonstrates overlap with the basal-like subtype. We broaden the scope of this topic by addressing a "repair-defective" rather than "BRCA1-like" phenotype. We discuss structural and functional aspects of key repair proteins including BRCA1, BRCA2, BRCA1 interacting protein C-terminal helicase 1, and partner and localizer of BRCA2 and describe the phenotypic consequences of their loss at the cellular, tissue, and organism level. We review potential mechanisms of repair pathway dysfunction in sporadic tumors and address how the identification of such defects may guide the application of repair-directed therapies.

Discovering moderate-risk breast cancer susceptibility genes

To date, five moderate-risk breast cancer susceptibility genes have been convincingly identified: CHEK2, ATM, BRIP1, PALB2, and NBS1. Moderate-risk breast cancer alleles confer increased breast cancer risks of two to fourfold compared to the 10% risk in the general population. In contrast to the high-risk BRCA1 and BRCA2 genes, moderate-risk genes typically have a limited number of variants that confer breast cancer risks. The prevalence of the variants usually varies widely among different geographical or ethnic populations, ranging from essentially absent up to 1.5% (i.e. 'rare' variants). Since moderate-risk breast cancer alleles are clinically not recognizable when inherited as single mutant, one usually encounters them in a polygenic setting and consequently in incomplete cosegregation with the breast cancer phenotype. As a result, discovery of moderate-risk breast cancer genes requires conclusive statistical evidence from association studies of hundreds of breast cancer cases and population-matched controls.

PALB2 mutations 1592delT and 229delT are not present in Korean breast cancer patients negative for BRCA1 and BRCA2 mutations

PALB2 is a recently discovered breast cancer susceptibility gene, and mutations in the gene have been demonstrated to confer about twofold higher risk of breast cancer. Truncating mutations in PALB2 gene have been identified in varied populations. However, PALB2's significance to breast cancer has not been investigated in the Korean population. In this study, we evaluated the frequency of PALB2 1592delT and 229delT mutations in 300 Korean breast cancer patients diagnosed with either familial or early-onset breast cancer. All patients were confirmed negative for BRCA1 and BRCA2 mutations. Neither 1592delT nor 229delT mutations was found in any of the study cohort. Our results imply that these mutations are absent or rare in Korean patients who are negative for BRCA1 and BRCA2 mutations. We found no evidence to recommend screening for these mutations in the Korean population. However, PALB2 mutations have been demonstrated infrequent and inhomogeneous across investigated populations. Thus, screening the whole PALB2 gene for novel mutations is required to elucidate its significance in predisposition to breast cancer in Korean women.

Mitotic homologous recombination maintains genomic stability and suppresses tumorigenesis

Mitotic homologous recombination promotes genome stability through the precise repair of DNA double-strand breaks and other lesions that are encountered during normal cellular metabolism and from exogenous insults. As a result, homologous recombination repair is essential during proliferative stages in development and during somatic cell renewal in adults to protect against cell death and mutagenic outcomes from DNA damage. Mutations in mammalian genes encoding homologous recombination proteins, including BRCA1, BRCA2 and PALB2, are associated with developmental abnormalities and tumorigenesis. Recent advances have provided a clearer understanding of the connections between these proteins and of the key steps of homologous recombination and DNA strand exchange.

A novel germline PALB2 deletion in Polish breast and ovarian cancer patients

Background

PALB2 protein was recently identified as a partner of BRCA1 and BRCA2 which determines their proper function in DNA repair.

Methods

Initially, the entire coding sequence of the PALB2 gene with exon/intron boundaries was evaluated by the PCR-SSCP and direct sequencing methods on 70 ovarian carcinomas. Sequence variants of interest were further studied on enlarged groups of ovarian carcinomas (total 339 non-consecutive ovarian carcinomas), blood samples from 334 consecutive sporadic and 648 consecutive familial breast cancer patients, and 1310 healthy controls from central Poland.

Results

Ten types of sequence variants were detected, and among them four novel polymorphisms: c.2996+58T>C in intron 9; c.505C>A (p.L169I), c.618T>G (p.L206L), both in exon 4; and c.2135C>T (A712V) in exon 5 of the PALB2 gene. Another two polymorphisms, c.212-58A>C and c.2014G>C (E672Q) were always detected together, both in cancer (7.5% of patients) and control samples (4.9% of controls, p = 0.2). A novel germline truncating mutation, c.509_510delGA (p.R170fs) was found in exon 4: in 2 of 339 (0.6%) unrelated ovarian cancer patients, in 4 of 648 (0.6%) unrelated familial breast cancer patients, and in 1 of 1310 controls (0.08%, p = 0.1, p = 0.044, respectively). One ovarian cancer patient with the PALB2 mutation had also a germline nonsense mutation of the BRCA2 gene.

Conclusions

The c.509_510delGA is a novel PALB2 mutation that increases the risk of familial breast cancer. Occurrence of the same PALB2 alteration in seven unrelated women suggests that c.509_510delGA (p.R170fs) is a recurrent mutation for Polish population.

The ups and downs of DNA repair biomarkers for PARP inhibitor therapies

PARP inhibitors are emerging as a valuable new drug class in the treatment of cancer. Recent discoveries make a compelling case for the complexity of DNA repair biomarker evaluation and underscore the need to examine at multiple biomarkers in a relational manner. This review updates the current trends in DNA repair biomarker strategies in use for the PARP inhibitors and describes the impact of many DNA repair biomarkers on PARP inhibitor benefit in the cancer clinic.

PALB2 variants in hereditary and unselected Finnish prostate cancer cases

BACKGROUND

PALB2 1592delT mutation is associated with increased breast cancer and suggestive prostate cancer (PRCA) risk in Finland. In this study we wanted to assess if any other PALB2 variants associate to increased PRCA risk and clinically describe patients with formerly found PALB2 1592delT mutation.

METHODS

Finnish families with two or more PRCA cases (n = 178) and unselected cases (n = 285) with complete clinical data were initially screened for variants in the coding region and splice sites of PALB2. Potentially interesting variants were verified in additional set of unselected cases (n = 463).

RESULTS

From our clinically defined sample set we identified total of six variants in PALB2. No novel variants among Finnish PRCA cases were found. Clinical characteristics of the variant carriers, including the previously described family carrying PALB2 1592delT, revealed a trend towards aggressive disease, which also applied to a few non-familial cases. Hypersensitivity to mitomycin C (MMC) of lymphoblasts from individuals from the family with 1592delT revealed haploinsufficiency among carriers with altered genotype.

CONCLUSIONS

Though any of the detected PALB2 variants do not associate to PRCA in population level in Finland it cannot be ruled out that some of these variants contribute to cancer susceptibility at individual level.

Subtypes of familial breast tumours revealed by expression and copy number profiling

Extensive expression profiling studies have shown that sporadic breast cancer is composed of five clinically relevant molecular subtypes. However, although BRCA1-related tumours are known to be predominantly basal-like, there are few published data on other classes of familial breast tumours. We analysed a cohort of 75 BRCA1, BRCA2 and non-BRCA1/2 breast tumours by gene expression profiling and found that 74% BRCA1 tumours were basal-like, 73% of BRCA2 tumours were luminal A or B, and 52% non-BRCA1/2 tumours were luminal A. Thirty-four tumours were also analysed by single nucleotide polymorphism-comparative genomic hybridization (SNP-CGH) arrays. Copy number data could predict whether a tumour was basal-like or luminal with high accuracy, but could not predict its mutation class. Basal-like BRCA1 and basal-like non-BRCA1 tumours were very similar, and contained the highest number of chromosome aberrations. We identified regions of frequent gain containing potential driver genes in the basal (8q and 12p) and luminal A tumours (1q and 17q). Regions of homozygous loss associated with decreased expression of potential tumour suppressor genes were also detected, including in basal tumours (5q and 9p), and basal and luminal tumours (10q). This study highlights the heterogeneity of familial tumours and the clinical consequences for treatment and prognosis.

Evaluation of variants in the CHEK2, BRIP1 and PALB2 genes in an Irish breast cancer cohort

It has been proposed that rare variants within the double strand break repair genes CHEK2, BRIP1 and PALB2 predispose to breast cancer. The aim of this study was to evaluate the prevalence of these variants in an Irish breast cancer cohort and determine their contribution to the development of breast cancer in the west of Ireland. We evaluated the presence of CHEK2_1100delC variant in 903 breast cancer cases and 1,016 controls. Six previously described variants within BRIP1 and five within PALB2 were screened in 192 patients with early-onset or familial breast cancer. Where a variant was evident, it was then examined in the remainder of our 711 unselected breast cancer cases. CHEK2_1100delC was found in 5/903 (0.5%) breast cancer cases compared to 1/1016 (0.1%) controls. One mutation at BRIP1 (2392 C>T) was identified in the early-onset/familial cohort. Examination of this variant in the remainder of our cohort (711 cases) failed to identify any additional cases. None of the previously described PALB2 variants were demonstrated in the early-onset/familial cohort. We show evidence of CHEK2_1100delC and BRIP1 2392 C>T within the Irish population. CHEK2_1100delC and BRIP1 mutations incidence in Ireland is similar to that found in other unselected breast cancer cohorts from northern European countries. We found no evidence to suggest that PALB2 mutation is an important breast cancer predisposition gene in this population.

A PALB2 germline mutation associated with hereditary breast cancer in Italy

Recently, it has been demonstrated that monoallelic PALB2 mutations predispose to familial breast cancer. We investigated the contribution of PALB2 mutations in a set of 132 Italian BRCA1/BRCA2-negative breast cancer families; one truncating PALB2 mutation, c.2257C>T, resulting in p.Arg753X, was identified in a woman and her daughter, with breast cancer diagnosed at 60 and 31 years old, respectively. This study supports the recent observation that PALB2 mutation are present, although infrequently, in familial BRCA1/BRCA2-negative breast cancer cases; moreover, it sustains latest evidences that some PALB2 mutations are associated with a substantially increased risk of breast cancer.

Mutational analysis of FANCL, FANCM and the recently identified FANCI suggests that among the 13 known Fanconi Anemia genes, only FANCD1/BRCA2 plays a major role in high-risk breast cancer predisposition

Fanconi Anemia (FA) is a rare recessive syndrome characterized by cellular hypersensitivity to DNA-cross-linking agents. To date, 13 FA complementation groups have been described and all 13 genes associated to each of these groups have been currently identified. Three of the known FA genes are also high-risk (FANCD1/BRCA2) or moderate-risk (FANCN/PALB2 and FANCJ/BRIP1) breast cancer susceptibility genes, which makes all members of the FA pathway particularly attractive breast cancer candidate genes. Most FA genes have been screened for mutations in breast cancer families negative for BRCA1/2 mutations but the role of FANCL, FANCM and the recently identified FANCI has not been evaluated to date. This fact and novel data sustaining greater functional relevance of the three genes within the FA pathway prompted us to scrutinize all coding sequences and splicing sites of FANCI, FANCL and FANCM in 95 BRCA1/2-negative index cases from Spanish high-risk breast cancer families. We identified 68 sequence variants of which 24 were coding and 44 non-coding. Six exonic and 26 non-coding variants had not been described previously. None of the coding changes caused clearly pathogenic changes and computational analysis of all non-described intronic variants did not revealed major impact in splicing. With the present study, all known FA genes have been evaluated within the context of breast cancer high-risk predisposition. Our results rule out a major role of FANCI, FANCL and FANCM in familial breast cancer susceptibility, suggesting that among the 13 known FA genes, only FANCD1/BRCA2 plays a major role in high-risk breast cancer predisposition.

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.

The Fanconi anemia/BRCA gene network in zebrafish: embryonic expression and comparative genomics

Fanconi anemia (FA) is a genetic disease resulting in bone marrow failure, high cancer risks, and infertility, and developmental anomalies including microphthalmia, microcephaly, hypoplastic radius and thumb. Here we present cDNA sequences, genetic mapping, and genomic analyses for the four previously undescribed zebrafish FA genes (fanci, fancj, fancm, and fancn), and show that they reverted to single copy after the teleost genome duplication. We tested the hypothesis that FA genes are expressed during embryonic development in tissues that are disrupted in human patients by investigating fanc gene expression patterns. We found fanc gene maternal message, which can provide Fanc proteins to repair DNA damage encountered in rapid cleavage divisions. Zygotic expression was broad but especially strong in eyes, central nervous system and hematopoietic tissues. In the pectoral fin bud at hatching, fanc genes were expressed specifically in the apical ectodermal ridge, a signaling center for fin/limb development that may be relevant to the radius/thumb anomaly of FA patients. Hatching embryos expressed fanc genes strongly in the oral epithelium, a site of squamous cell carcinomas in FA patients. Larval and adult zebrafish expressed fanc genes in proliferative regions of the brain, which may be related to microcephaly in FA. Mature ovaries and testes expressed fanc genes in specific stages of oocyte and spermatocyte development, which may be related to DNA repair during homologous recombination in meiosis and to infertility in human patients. The intestine strongly expressed some fanc genes specifically in proliferative zones. Our results show that zebrafish has a complete complement of fanc genes in single copy and that these genes are expressed in zebrafish embryos and adults in proliferative tissues that are often affected in FA patients. These results support the notion that zebrafish offers an attractive experimental system to help unravel mechanisms relevant not only to FA, but also to breast cancer, given the involvement of fancj (brip1), fancn (palb2) and fancd1 (brca2) in both conditions.

Cellular and molecular consequences of defective Fanconi anemia proteins in replication-coupled DNA repair: mechanistic insights

The Fanconi anemia (FA) molecular network consists of 15 "FANC" proteins, of which 13 are associated with mutations in patients with this cancer-prone chromosome instability disorder. Whereas historically the common phenotype associated with FA mutations is marked sensitivity to DNA interstrand crosslinking agents, the literature supports a more global role for FANC proteins in coping with diverse stresses encountered by replicative polymerases. We have attempted to reconcile and integrate numerous observations into a model in which FANC proteins coordinate the following physiological events during DNA crosslink repair: (a) activating a FANCM-ATR-dependent S-phase checkpoint, (b) mediating enzymatic replication-fork breakage and crosslink unhooking, (c) filling the resulting gap by translesion synthesis (TLS) by error-prone polymerase(s), and (d) restoring the resulting one-ended double-strand break by homologous recombination repair (HRR). The FANC core subcomplex (FANCA, B, C, E, F, G, L, FAAP100) promotes TLS for both crosslink and non-crosslink damage such as spontaneous oxidative base damage, UV-C photoproducts, and alkylated bases. TLS likely helps prevent stalled replication forks from breaking, thereby maintaining chromosome continuity. Diverse DNA damages and replication inhibitors result in monoubiquitination of the FANCD2-FANCI complex by the FANCL ubiquitin ligase activity of the core subcomplex upon its recruitment to chromatin by the FANCM-FAAP24 heterodimeric translocase. We speculate that this translocase activity acts as the primary damage sensor and helps remodel blocked replication forks to facilitate checkpoint activation and repair. Monoubiquitination of FANCD2-FANCI is needed for promoting HRR, in which the FANCD1/BRCA2 and FANCN/PALB2 proteins act at an early step. We conclude that the core subcomplex is required for both TLS and HRR occurring separately for non-crosslink damages and for both events during crosslink repair. The FANCJ/BRIP1/BACH1 helicase functions in association with BRCA1 and may remove structural barriers to replication, such as guanine quadruplex structures, and/or assist in crosslink unhooking.

PALB2 functionally connects the breast cancer susceptibility proteins BRCA1 and BRCA2

BRCA1 and BRCA2 are prominently associated with inherited breast and ovarian cancer. The encoded proteins function in DNA damage responses, but no functional link between BRCA1 and BRCA2 has been established. We show here that PALB2 physically and functionally connects BRCA1 and BRCA2 into a DNA damage response network that also includes the RAD51 recombinase. PALB2 directly binds BRCA1, as determined with bacterially expressed fragments of each protein. Furthermore, PALB2 independently interacts with BRCA1 and BRCA2 through its NH2 and COOH termini, respectively. Critically, two point mutants (L21P and L24P) of the PALB2 coiled-coil domain or an NH2-terminal deletion (Delta1-70) disrupt its interaction with BRCA1. We have reconstituted PALB2-deficient cells with PALB2Delta1-70, PALB2-L21P, or PALB2-L24P, or with COOH-terminally truncated PALB2 that is deficient for interaction with BRCA2. Using extracts from these cells, we find that PALB2 mediates the physical interaction of BRCA2 with a COOH-terminal fragment of BRCA1. Analysis of the assembly of foci in these cells by BRCA1, PALB2, BRCA2, and RAD51 suggests that BRCA1 recruits PALB2, which in turn organizes BRCA2 and RAD51. Resistance to mitomycin C and the repair of DNA double-strand breaks by homologous recombination require the interaction of PALB2 with both BRCA1 and BRCA2. These results suggest that BRCA1 and BRCA2 cooperate in DNA damage responses in a PALB2-dependent manner, and have important implications for the genesis of breast/ovarian cancer and for chemotherapy with DNA interstrand cross-linking agents.

The Fanconi anemia family of genes and its correlation with breast cancer susceptibility and breast cancer features

Fanconi anemia (FA) family of proteins participates in the DNA repair pathway by homologous recombination, and it is currently formed by 13 genes. Some of these proteins also confer susceptibility to hereditary breast and ovarian cancer (HBOC), since FANCD1 is the BRCA2 breast cancer susceptibility gene, and FANCN/PALB2 and FANCJ/BRIP1 explain 2% of non-BRCA1/2 HBOC families. Thus, there is an important connection between FA and BRCA pathways. In a previous case-control association study analysing FANCA, FANCD2 and FANCL, we reported an association between FANCD2 and sporadic breast cancer (BC) risk (OR = 1.35). In order to know whether variants in other FA genes could also be involved in this association, we have extended our study with the rest of FA genes and some others implicated in the BRCA pathway. We have also analyzed the correlation with survival, nodal metastasis and hormonal receptors (ER- and PR-). A total of 61 SNPs in ten FA genes (FANC-B, -C, -D1, -E, -F, -G, -I, -J, -M, -N) and five FA related genes (ATM, ATR, BRCA1, H2AX and USP1) were studied in a total of 547 consecutive and nonrelated sporadic BC cases and 552 unaffected controls from the Spanish population. Association analyses reported marginal statistically significant results with the minor allele of intronic SNPs in three genes: BRCA1, BRCA2/FANCD1, and ATM. Survival association with SNPs on FANCC and BRCA2/FANCD1 genes were also reported. Sub-group analyses revealed associations between SNPs on FANCI and ATM and nodal metastasis status and between FANCJ/BRIP1 and FANCN/PALB2 and PR- status.

PALB2 regulates recombinational repair through chromatin association and oligomerization

Maintenance of genomic stability ensures faithful transmission of genetic information and helps suppress neoplastic transformation and tumorigenesis. Although recent progress has advanced our understanding of DNA damage checkpoint regulations, little is known as to how DNA repair, especially the RAD51-dependent homologous recombination repair pathway, is executed in vivo. Here, we reveal novel properties of the BRCA2-associated protein PALB2 in the assembly of the recombinational DNA repair machinery at DNA damage sites. Although the chromatin association of PALB2 is a prerequisite for subsequent BRCA2 and RAD51 loading, the focal accumulation of the PALB2 x BRCA2 x RAD51 complex at DSBs occurs independently of known DNA damage checkpoint and repair proteins. We provide evidence to support that PALB2 exists as homo-oligomers and that PALB2 oligomerization is essential for its focal accumulation at DNA breaks in vivo. We propose that both PALB2 chromatin association and its oligomerization serve to secure the BRCA2 x RAD51 repair machinery at the sites of DNA damage. These attributes of PALB2 are likely instrumental for proficient homologous recombination DNA repair in the cell.

The breast cancer susceptibility mutation PALB2 1592delT is associated with an aggressive tumor phenotype

PURPOSE

To determine the effect of the breast cancer susceptibility mutation PALB2 1592delT on tumor phenotype and patient survival.

EXPERIMENTAL DESIGN

We defined the PALB2 mutation status in 947 familial and 1,274 sporadic breast cancer patients and 1,079 population controls, and compared tumor characteristics and survival in mutation carriers relative to other familial and sporadic cases and to 79 BRCA1 and 104 BRCA2 mutation carrier cases.

RESULTS

The PALB2 1592delT mutation was found in 19 familial [2.0%; odds ratio, 11.03; 95% confidence interval (95% CI), 2.65-97.78; P < 0.0001] and eight sporadic patients (0.6%; odds ratio, 3.40; 95% CI, 0.68-32.95; P = 0.1207) compared with two (0.2%) control individuals. Tumors of the PALB2 mutation carriers presented triple negative (estrogen receptor negative/progesterone receptor negative/HER negative) phenotype more often (54.5%; P < 0.0001) than those of other familial (12.2%) or sporadic (9.4%) breast cancer patients. They were also more often of higher grade (P = 0.0027 and P = 0.0017, respectively) and had higher expression of Ki67 (P = 0.0004 and P = 0.0490, respectively). Carrying a PALB2 mutation was also associated with reduced survival, especially in familial cases (hazard ratio, 2.30; 95% CI, 1.01-5.24; P = 0.0466) and among familial patients with HER2-negative tumors (hazard ratio, 4.57; 95% CI, 1.96-10.64; P = 0.0004). Carrying a BRCA2 mutation was also found to be an independent predictor of poor survival at 10-year follow-up (P = 0.04).

CONCLUSIONS

The PALB2 1592delT mutation has a strong effect on familial breast cancer risk. The tumors rising in patients carrying this mutation manifest a phenotype associated with aggressive disease. Our results also suggest a significant impact of carrying a BRCA2 mutation on long-term breast cancer survival.

Hereditary breast cancer: from bench to bedside

PURPOSE OF REVIEW

The proportion of breast cancers directly attributable to determinant hereditary factors is estimated to be 5-10%. A number of recent findings with regard to hereditary breast cancer should affect the criteria and scope of routine genetic testing and, soon, breast cancer therapy.

RECENT FINDINGS

The number of genes causing genetic cancer has expanded, mostly with genes that encode proteins that function in the BRCA1/2 pathways. The risk level associated with some genes is still under investigation, but is high for specific mutations. Some mutant alleles occur frequently, some are rare. High-throughput technologies will progressively allow investigating all genes involved in genetic (breast) cancer risks in all individuals for whom this information could be relevant. This and the emerging novel treatment options specific for cancers in mutation carriers will oblige us to progressively drop all currently used selection criteria such as familial phenotype for genomic testing. A major challenge remains the effective penetration of this knowledge in the professional and lay community, the broad application and financing of this high-throughput technology, and the identification of as yet unknown breast cancer predisposition genes.

SUMMARY

The assessment of breast cancer predisposition genes, previously only an optional predictive genetic test, is growing in importance as it also becomes a therapeutic predictive test.

PALB2 is an integral component of the BRCA complex required for homologous recombination repair

Mutations in breast cancer susceptibility gene 1 and 2 (BRCA1 and BRCA2) predispose individuals to breast and ovarian cancer development. We previously reported an in vivo interaction between BRCA1 and BRCA2. However, the biological significance of their association is thus far undefined. Here, we report that PALB2, the partner and localizer of BRCA2, binds directly to BRCA1, and serves as the molecular scaffold in the formation of the BRCA1-PALB2-BRCA2 complex. The association between BRCA1 and PALB2 is primarily mediated via apolar bonding between their respective coiled-coil domains. More importantly, BRCA1 mutations identified in cancer patients disrupted the specific interaction between BRCA1 and PALB2. Consistent with the converging functions of the BRCA proteins in DNA repair, cells harboring mutations with abrogated BRCA1-PALB2 interaction resulted in defective homologous recombination (HR) repair. We propose that, via its direct interaction with PALB2, BRCA1 fine-tunes recombinational repair partly through its modulatory role in the PALB2-dependent loading of BRCA2-RAD51 repair machinery at DNA breaks. Our findings uncover PALB2 as the molecular adaptor between the BRCA proteins, and suggest that impaired HR repair is one of the fundamental causes for genomic instability and tumorigenesis observed in patients carrying BRCA1, BRCA2, or PALB2 mutations.

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.

PALB2 links BRCA1 and BRCA2 in the DNA-damage response

BRCA1 and BRCA2 are often mutated in familial breast and ovarian cancer. Both tumor suppressors play key roles in the DNA-damage response. However, it remains unclear whether these two tumor suppressor function together in the same DNA-damage response pathway. Here, we show that BRCA1 associates with BRCA2 through PALB2/FANCN, a major binding partner of BRCA2. The interaction between BRCA1 and BRCA2 is abrogated in PALB2-deficient Fanconi anemia cells and in the cells depleted of PALB2 by small interfering RNA. Moreover, we show that BRCA1 promotes the concentration of PALB2 and BRCA2 at DNA-damage sites and the interaction between BRCA1 and PALB2 is important for the homologous recombination repair. Taken together, our results indicate that BRCA1 is an upstream regulator of BRCA2 in the DNA-damage response, and PALB2 is the linker between BRCA1 and BRCA2.

Molecular profiles of hereditary epithelial ovarian cancers and their implications for the biology of this disease

BRCA1 and BRCA2 germline mutations account for the majority of hereditary ovarian cancers and comprise 10% of total cases. Ovarian cancers arising from these mutations exhibit both overlapping and distinct clinical and molecular features. The expression profiles of sporadic ovarian cancers show similarities to those of BRCA1 and BRCA2-related tumors suggesting that BRCA-related pathways may be involved in their development as well. The purpose of this review is to consider the available data on ovarian cancers in the context of other investigations of BRCA-related transcriptional alterations, and highlight areas for future research.

Low prevalence of CDKN2A/ARF mutations among early-onset cancers of breast, pancreas and malignant melanoma in Poland

In this report the contribution of CDKN2A/ARF germline mutations to early-onset cancers of the breast, pancreas and malignant melanoma was examined. We screened 66 women with breast cancer diagnosed at age 30 and below, 72 melanoma patients with the median age at diagnosis < or = 40 years and 51 pancreatic cancer patients diagnosed under the age of 50 years. In the total set of 189 patients we found a novel change Pro48Arg (nt 143 c > g), a novel intronic change IVS1+36 g>c and two common variants A148T and IVS3+29 c>g. The results of this study revealed a paucity of mutations in CDKN2A/ARF suggesting that in the Polish population this gene does not contribute significantly to early-onset breast cancer, pancreatic cancer and malignant melanoma.

Defects of FA/BRCA pathway in lymphoma cell lines

The aim was to find the possible relationship between defects in the FA/BRCA pathway of genomic maintenance and potential pathogenesis of T and B cell lymphoma. We screened 29 cell lines derived from diverse subtypes of lymphoma for possible FA pathway defects. The results indicated: no defect in FANCD2 ubiquitination, BRCA2 and FANCJ expression; absence of FANCN protein in three cell lines: HT, Sudhl4 and JEKO-1. This absence was correlated with enhanced MMC-induced G2 arrest, growth inhibition and high chromosomal breakage rate in the three cell lines. We only found one substitution in HT and JEKO-1 exon-5a fragment: c.1769C > T, p. A590V. But in another lymphoma cell line Sudhl4 with FANCN absence, we have not found any mutation. In conclusion, this mutation maybe the reason which caused FANCN protein expression absent or made the protein very unstable and lose its function in HT and JEKO-1 cell lines.

Association of common PALB2 polymorphisms with breast cancer risk: a case-control study

PURPOSE

The PALB2 gene has an essential role in BRCA2-mediated DNA double-strand break repair and intra-S phase DNA damage checkpoint control, and its mutations are moderately associated with breast cancer susceptibility. This study was designed to investigate the common variants of PALB2 and their association with breast cancer risk.

EXPERIMENTAL DESIGN

Four single nucleotide polymorphisms (SNP; rs249954, rs249935, rs120963, and rs16940342) which tagged all 19 of the reported SNPs (minor allele frequency >0.05) covering PALB2 were selected and genotyped in 1,049 patients with breast cancer and 1,073 cancer-free controls in a female Chinese population.

RESULTS

Based on the multiple hypothesis testing with the Benjamini-Hochberg method, tagging SNPs (tSNP) rs249954, rs120963, and rs16940342 were found to be associated with an increase of breast cancer risk (false discovery rate-adjusted P values of 0.004, 0.028, and 0.049, respectively) under the dominant model. tSNP rs249954 was associated with a 36% increase of breast cancer risk [adjusted odds ratio (OR), 1.36; 95% confidence intervals (CI), 1.13-1.64; P = 0.001; TT/TC versus CC genotypes]. The adjusted OR for rs120963 was 1.25 (95% CI, 1.04-1.49; P = 0.014; CC/CT versus TT genotypes). For rs16940342, the adjusted OR was 1.21 (95% CI, 1.02-1.45; P = 0.037; GG/GA versus AA genotypes). Based on an additive model, tSNPs rs249954 and rs120963 were associated with an increase of breast cancer risk (P = 0.005 and 0.019; respectively), with the false discovery rate-adjusted P values being 0.020 and 0.038, respectively.

CONCLUSIONS

Our data suggest that the variants of PALB2 confer low-penetrance breast cancer susceptibility in a Chinese population.

Penetrance analysis of the PALB2 c.1592delT founder mutation

PURPOSE

PALB2 is a recently identified breast cancer susceptibility gene. We have previously identified in the Finnish population a PALB2 c.1592delT founder truncation mutation that is associated with an increased risk of breast cancer. In the present study, we wanted to assess in more detail the increased risk (hazard ratio, HR) and the age-specific cumulative risk (penetrance) of c.1592delT with regard to susceptibility to breast and other forms of cancer.

EXPERIMENTAL DESIGN

Modified segregation analyses fitted under maximum likelihood theory were used to estimate age-specific cumulative risks and HRs using the families of mutation carriers identified from a consecutive series of breast cancer cases unselected for age at onset or family history.

RESULTS

We found a substantially increased risk of breast cancer [HR, 6.1; 95% confidence interval (95% CI), 2.2-17.2; P = 0.01] equivalent to a 40% (95% CI, 17-77) breast cancer risk by age 70 years, comparable to that for carriers of mutations in BRCA2. We found marginal evidence (P = 0.06) that the HR for breast cancer decreased with age by 4.2% per year (95% CI, 0.2-8.1), from 7.5-fold at age 30 years to 2.0-fold at age 60 years.

CONCLUSIONS

Our results suggest that it may be appropriate to offer PALB2 c.1592delT mutation testing to Finnish women with breast cancer, especially those with an early age at onset or a family history of breast or related cancers, and to offer carriers the option of participation in extended disease surveillance programs.