新疆地区维吾尔族乳腺癌BRCA1基因突变分析

目的研究新疆地区维吾尔族乳腺癌患者BRCA1基因突变情况及突变位置。方法选取70例维吾尔族乳腺癌根治标本,对照组为32例维汉族乳腺良性病变（纤维腺病及纤维腺瘤）及乳腺癌旁非癌组织;应用PCR-单链构象多态性和DNA序列测定的方法检测BRCA1基因突变。结果（1）70例维吾尔族乳腺癌中发现9例BRCA1突变的12个新位点。（2）70例维吾尔族乳腺癌BRCA1的突变率为12.86%（9/70）,22例维吾尔族早发性乳腺癌（≤35岁）BRCA1突变率为31.82%（7/22）。维吾尔族早发性乳腺癌BRCA1突变率（7/22）高于维吾尔族晚发性乳腺癌（2/48）,差异有统计学意义（χ^2=10.295,P〈0.01）。（3）70例维吾尔族乳腺癌中发现9例BRCA1基因核苷酸多态性位点,其中8例多态性位点均为3232A〉G。（4）2例双侧乳腺癌中均检测出BRCA1基因的突变。结论BRCA1突变可能与新疆维吾尔族乳腺癌尤其是维吾尔族早发性乳腺癌及双侧乳腺癌的发生密切相关。     

Immunolocalization of BRCA1 protein in normal breast tissue and sporadic invasive ductal carcinomas: a correlation with other biological parameters

AIM: BRCA1, a nuclear phosphoprotein, normally functions as a negative regulator of the cell cycle and may be an active inhibitor of neoplastic progression. Mutation of the BRCA1 gene has been demonstrated in 80% of familial breast cancer. Decreased mRNA levels or aberrant subcellular locations of BRCA1 have been identified in breast cancer lines and in sporadic cases of breast cancer tissues. The expression of BRCA1 in large series of variously differentiated breast carcinomas with correlation with other biological parameters has not been clarified. METHODS AND RESULTS: The BRCA1 expression in normal breast tissue (n = 15) and in sporadic cases of invasive ductal carcinoma (n=108) was determined using immunohistochemistry. BRCA1 expression was correlated with other prognostic parameters including p53, c-erbB-2, bcl-2, oestrogen receptor (ER), histological grade, tumour size, axillary lymph node status and age. BRCA1 was exclusively (100%) localized in the nuclei of normal ductal and lobular epithelia. However, this nuclear expression pattern was variable in breast carcinoma (76.8%). Loss of nuclear BRCA1 expression (22 of 108 cases, 20.4%) correlated well with high histological grade (P<0.025) and bcl-2-negative tumours (P<0.05) and frequently in ER-negative tumours. CONCLUSION: BRCA1 nuclear expression could be considered to represent the normal or physiological phenotype. Complete loss of BRCA1 nuclear expression in breast cancer and its correlation with other poor prognostic markers suggest that BRCA1 expression may play an important role in the pathogenesis and prognosis of sporadic breast carcinoma. Altered BRCA1 phenotype may therefore provide an additional prognostic parameter for breast cancer.     

Mutational analysis of the BRCA1-interacting genes ZNF350/ZBRK1 and BRIP1/BACH1 among BRCA1 and BRCA2-negative probands from breast-ovarian cancer families and among early-onset breast cancer cases and reference individuals

Two potential breast cancer susceptibility genes, encoding the BRCA1-interacting proteins ZNF350 (or ZBRK1) and BRIP1 (or BACH1), have been identified in yeast two-hybrid screens. We sequenced these genes in probands from 21 families with potentially inherited breast/ovarian cancer, all of which were negative for BRCA1/BRCA2 mutations. Families had at least one case of male breast cancer, two cases of ovarian cancer, or three or more cases of breast and ovarian cancer. In addition, 58 early-onset (before age 35) breast cancer cases and 30 reference individuals were analyzed. Of 17 variants detected in ZBRK1, a missense mutation Val524Ile was identified in the proband of one high-risk family, but no other family members were available for testing. Of 25 variants identified in BRIP1, in addition to four common silent or missense mutations, we identified Gln540Leu, a non-conservative amino acid change, in a single familial proband with inflammatory breast cancer, but this mutation was not present in her three relatives with breast cancer. Haplotype analysis suggests that all ZBRK1 SNPs fall within a single block with two SNPs capturing 92% of the haplotype diversity, while the BRIP1 SNPs fall in two blocks, with five SNPs capturing 89% of the haplotype diversity. Based on sequencing of ZBRK1 and BRIP1 in 21 BRCA1/2-negative probands from inherited breast/ovarian cancer families, it appears unlikely that mutations in these genes account for a significant fraction of inherited breast cancer. Further analysis in unselected cases will be required to know whether the identified variants play a role in genetic predisposition to breast cancer in the general population. Hum Mutat 22:121-128, 2003. Published 2003 Wiley-Liss, Inc.     

维吾尔族及汉族早发性乳腺癌 BRCA1基因突变分析

目的研究维吾尔族及汉族早发性乳腺癌患者BRCA1突变情况及突变位置。方法选取35例维吾尔族及汉族早发性乳腺癌根治标本（其中维吾尔族早发性乳腺癌22例,汉族乳腺癌13例）,对照组为32例维汉族乳腺良性病变（纤维腺病及纤维腺瘤）及乳腺癌旁非癌组织;运用PCR—SSCP和DNA序列测定的方法检测BRCA1基因突变。结果（1）35例新疆早发性乳腺癌（≤35岁）BRCA1突变率为22．86％（8／35）,22例维吾尔族早发性乳腺癌BRCA1突变率为31．82％（7／22）。（2）35例新疆早发性乳腺癌中发现8例BRCA1突变的12个新位点,其中2例突变位点IVS20-68insA均为维吾尔族早发性乳腺癌患者。（3）35例新疆早发性乳腺癌中发现7例BRCA1基因核苷酸多态性,对照组32例维吾尔族及汉族乳腺癌旁非癌组织及乳腺良性病变中仅发现1例BRCA1基因核苷酸的多态性。结论BRCA1突变可能与新疆早发性乳腺癌尤其是维吾尔族早发性乳腺癌密切相关,其突变位点IVS20—68insA可能是新疆维吾尔族早发性乳腺癌的遗传易感性位点,尚需扩大样本进一步研究证实。     

Characterization of ten novel and 13 recurring BRCA1 and BRCA2 germline mutations in Italian breast and/or ovarian carcinoma patients. Mutations in brief no. 178. Online

Germline mutations in the BRCA1 and BRCA2 genes are associated with approximately 80% of families with a high incidence of breast and/or ovarian cancers (OMIM database reference numbers: 113705, 600185). Furthermore, constitutional mutations in the these genes have been reported in women with early-onset breast carcinoma and without family history of cancer. We analyzed by protein truncation test (PTT) and single strand conformation polymorphism (SSCP) followed by sequence analysis, BRCA1 exons 11 and 20 and BRCA2 exons 10 and 11 in 142 Italian cancer patients. These included six male breast cancer cases, 61 women with breast carcinoma diagnosed before 36 years old and selected independently of family history of breast cancer and 75 familial breast and/or ovarian cancer patients. In a previous report, we described 11 different BRCA1 mutations in a subset of 70 cases. Here, we report the characterization of 23 additional mutations, 14 in BRCA1 and 9 in BRCA2, subsequently identified. Ten mutations were not previously described, while the other 13 were recurrent. Of the 61 women with early-onset breast cancer, 11 carried a germline mutation in BRCA1 (18.0%) and four in BRCA2 (6.6%). These frequencies indicate that BRCA1/BRCA2 genetic tests should be advised to women with breast cancer diagnosed at early age, independently of family history of cancer.     

Allelic imbalance in BRCA1 and BRCA2 gene expression is associated with an increased breast cancer risk

The contribution of BRCA1 and BRCA2 to familial and non-familial forms of breast cancer has been difficult to accurately estimate because of the myriad of potential genetic and epigenetic mechanisms that can ultimately influence their expression and involvement in cellular activities. As one of these potential mechanisms, we investigated whether allelic imbalance (AI) of BRCA1 or BRCA2 expression was associated with an increased risk of developing breast cancer. By developing a quantitative approach utilizing allele-specific real-time PCR, we first evaluated AI caused by nonsense-mediated mRNA decay in patients with frameshift mutations in BRCA1 and BRCA2. We next measured AI for BRCA1 and BRCA2 in lymphocytes from three groups: familial breast cancer patients, non-familial breast cancer patients and age-matched cancer-free females. The AI ratios of BRCA1, but not BRCA2, in the lymphocytes from familial breast cancer patients were found to be significantly increased as compared to cancer-free women (BRCA1: 0.424 versus 0.211, P = 0.00001; BRCA2: 0.206 versus 0.172, P = 0.38). Similarly, the AI ratios were greater for BRCA1 and BRCA2 in the lymphocytes of non-familial breast cancer cases versus controls (BRCA1: 0.353, P = 0.002; BRCA2: 0.267, P = 0.03). Furthermore, the distribution of under-expressed alleles between cancer-free controls and familial cases was significantly different for both BRCA1 and BRCA2 gene expression (P < 0.02 and P < 0.02, respectively). In conclusion, we have found that AI affecting BRCA1 and to a lesser extent BRCA2 may contribute to both familial and non-familial forms of breast cancer.     

Expression of BRCA1 protein in breast cancer and its prognostic significance

BRCA1 is a tumor suppressor gene which, when mutated, is associated with the development of hereditary breast cancers. In sporadic tumors, although inherent gene mutations are rare, loss of BRCA1, resulting from reduced expression or incorrect subcellular localization, is postulated to be important. The purpose of the current study was to examine the expression and localization of BRCA1 protein and to assess its prognostic value, in a well-characterized series of unselected breast carcinomas. We have examined BRCA1 in a series of invasive breast carcinoma (1940 cases) using tissue microarray and immunohistochemistry, to evaluate its expression pattern and to correlate this with clinicopathologic variables and patient outcome. In breast cancer, complete loss of nuclear expression was observed in 223 cases (15%) and cytoplasmic expression was found in 541 breast cancers (36.6%). Absent or reduced nuclear BRCA1 expression was observed more frequently in ductal carcinoma of no special type and medullary-like carcinoma and less frequently in lobular and tubular mixed carcinomas. It was also associated with high-grade, advanced lymph node stage, larger size, vascular invasion, negative estrogen receptor, progesterone receptor and androgen receptor expression, and positive p53 and P-cadherin expression, and with the basal-like class of breast cancer. Altered BRCA1 was associated with shorter disease-free interval. Cytoplasmic expression was also associated with development of recurrence and positive EGFR and HER2 expression. It showed an inverse association with survival particularly in low-grade, small-size, and estrogen receptor-positive subgroups. In the grade 1 subgroup, multivariate analysis with adjustment for other prognostic factors showed that cytoplasmic expression of BRCA1 was an independent predictor of disease-free interval. BRCA1 alteration may play a significant role in the development and progression of breast cancer. Immunohistochemical assessment of BRCA1 expression could provide additional clinically relevant information in routine classification of breast cancer.     

The analysis of BRCA1 mutations in eastern Chinese patients with early onset breast cancer and affected relatives

To study the BRCA1 mutations in eastern Chinese patients with early onset breast cancer and affected relatives, 41 patients' genomic DNA from peripheral mononuclear blood cells was studied by using single strand conformational polymorphism (SSCP) and DNA sequencing. The BRCA1 mutations were detected in the whole gene sequence. Three novel disease-causing mutations (c.582C>T, c.735C>T and c.2790delT) occurred in all the patients. Two occurred in the patients younger than 35 years old (9.1%) and one in the patients with affected relatives (5%). Additional sequence variants identified included a novel missense mutation of unknown significance and six polymorphisms. The prevalence of BRCA1 mutations in Chinese patients in Shanghai with early onset breast cancer is similar to that observed in western women, but the incidence of mutations in breast cancer patients in Shanghai with affected relatives isn't as high as that in western women.     

BRCA1-methylated sporadic breast cancers are BRCA-like in showing a basal phenotype and absence of ER expression

BRCA1 mutations have been associated with hereditary breast cancer only. Recent studies indicate that a subgroup of sporadic breast cancer might also be associated with reduction in BRCA1 mRNA levels and protein expression. However, the mechanism of reduced mRNA and protein expression is yet not fully elucidated. This study aims to assess BRCA1 protein expression and the role of BRCA1 promoter methylation in sporadic breast cancer in North Indian population and to correlate these with known prognostic factors and molecular profiles of breast cancer. BRCA1 protein expression was normal (>50?% tumour cells) in 41 (43?%) cases, reduced (20-50?% tumour cells) in 33 (35?%) cases and absent/markedly reduced (<20?% tumour cells) in 21 (22.1?%) cases. Cases which were negative for BRCA1 protein were more frequently positive for basal markers (29 versus 5?%) and were more often ER-negative (62 versus 39?%) than BRCA1-positive tumours. Methylation of BRCA1 promoter region was seen in 11/45 cases (24?%). All 11 cases showing BRCA1 methylation had absent (eight cases) or reduced (three cases) BRCA1 protein expression. BRCA1 protein-negative tumours were more frequently basal marker-positive and ER-negative, highlighting the 'BRCAness' of sporadic breast cancer with loss of BRCA1 protein expression through promoter hypermethylation similar to hereditary breast cancer with BRCA1 mutations. Loss of BRCA1 in sporadic breast cancer suggests that therapeutics targeting BRCA1 pathway in hereditary breast cancer like PARP inhibitors might be used as therapeutic targets for sporadic breast tumours.     

BRCA2 germline mutations in Cypriot patients with familial breast/ovarian cancer

Germline mutations in the BRCA2 gene have been shown to be associated with familial female and male breast cancer. Mutations occur throughout the entire coding region of the gene, and there is considerable ethnic and geographical diversity in the deleterious mutations detected in different populations. No data exist on the role of the BRCA2 gene in the Cypriot population. In this study we present the results of characterizing mutations in the BRCA2 gene, in 26 Cypriot families with multiple cases of breast/ovarian cancer. The entire coding region, including splice sites, of BRCA2 were sequenced using cycle sequencing. In total 29 BRCA2 variants were detected which include 3 truncating mutations, 8 missense mutations, 6 polymorphisms and 12 intronic variants. The 3 truncating mutations are frameshift mutation 8984delG (exon 22), and two nonsense mutations, namely C1913X (exon 11) which is a novel mutation, and K3326X (exon 27). It is of interest that frameshift mutation 8984delG was the most frequent, since it was detected in 5 patients from three different families. Among the 6 polymorphisms detected, polymorphism T77T is novel and similarly 4 of the 12 intronic variants were also novel, namely IVS1+8G>A, IVS1-96insA, IVS4+36A>G and IVS11-51G>T. These results show that deleterious BRCA2 mutations, occur at the same frequency, about 20%, in Cypriot families, as that recorded in other European populations. We conclude that the BRCA2 gene plays a significant role in the familial breast cancer phenotype in the Cypriot population.     

Germline BRCA1 alterations in a population-based series of ovarian cancer cases

The objective of this study was to provide more accurate frequency estimates of breast cancer susceptibility gene 1 ( BRCA1 ) germline alterations in the ovarian cancer population. To achieve this, we determined the prevalence of BRCA1 alterations in a population-based series of consecutive ovarian cancer cases. This is the first population-based ovarian cancer study reporting BRCA1 alterations derived from a comprehensive screen of the entire coding region. One hundred and seven ovarian cancer cases were analyzed for BRCA1 alterations using the RNase mismatch cleavage assay followed by direct sequencing. Two truncating mutations, 962del4 and 3600del11, were identified. Both patients had a family history of breast or ovarian cancer. Several novel as well as previously reported uncharacterized variants were also identified, some of which were associated with a family history of cancer. The frequency distribution of common polymorphisms was determined in the 91 Caucasian cancer cases in this series and 24 sister controls using allele-specific amplification. The rare form of the Q356R polymorphism was significantly ( P = 0.03) associated with a family history of ovarian cancer, suggesting that this polymorphism may influence ovarian cancer risk. In summary, our data suggest a role for some uncharacterized variants and rare forms of polymorphisms in determining ovarian cancer risk, and highlight the necessity to screen for missense alterations as well as truncating mutations in this population.     

Loss of markers linked to BRCA1 precedes loss at important cell cycle regulatory genes in epithelial ovarian cancer

Advanced-stage epithelial ovarian cancers (EOC) from 114 patients were assessed for loss of heterozygosity (LOH or allelic imbalance) at several tumor suppressor gene loci as an initial step in identifying gene alterations important to the development of these tumors. The highest frequency of loss, 84% (86 of 102 cases), was observed for markers mapping near or within BRCA1; other significant frequencies of LOH were observed for loci mapping near or within CDKN2A/CDKN2B (56%), BRCA2 (61%), RB1 (67%), or TP53 (73%). No instance of TP53 LOH was observed without simultaneous allelic imbalance at the BRCA1 region (P = 0.0005). LOH of CDKN2 without loss near the BRCA1 region was seen in only 2 of 75 cases (P < 0.0001), and RB1 LOH without BRCA1 loss occurred in only 1 of 35 tumors (P = 0.0703). These data suggest that LOH of BRCA1, or a closely linked locus, precedes the loss of CDKN2, TP53, and RB1, and imply that inactivation of a tumor suppressor gene in this region is an important early step in the development of these tumors.     

High incidence of cancer in a family segregating a mutation of the ATM gene: possible role of ATM heterozygosity in cancer

ATM mutations predispose cells to malignancy by promoting chromosomal instability. We have identified a family with multiple cancers that segregates a mutant allele of ATM, IVS61+2insTA, which causes skipping of exon 61 in the mRNA, as well as a previously undescribed polymorphism, IVS61+104C(54):T(46). The mutation was inherited by two sisters, one who developed breast cancer at age 39 and the second at age 44, from their mother, who developed kidney cancer at age 67. Molecular studies were undertaken to determine the role of the ATM gene in the development of cancer in this family. Studies of irradiated lymphocytes from both sisters revealed elevated numbers of chromatid breaks, typical of A-T heterozygotes. Studies on lymphoblastoid cell lines established from these individuals revealed abnormal p53 induction and apoptosis after DNA damage. Loss of heterozygosity (LOH) in the ATM region of chromosome 11q23.1 showed that the normal ATM allele was lost in the breast tumor of the older sister. LOH was not seen at the BRCA1 or BRCA2 loci. BRCA2 is not likely to be a cancer-predisposing gene in this family because each sister inherited different chromosomes 13 from each parent. The sisters share their maternal BRCA1 allele, although no mutation in this gene was detected in the family. Our findings suggest that haploinsufficiency at ATM may promote tumorigenesis, even though LOH at the locus supports a more classic two-hit tumor suppressor gene model.     

Novel somatic mutations in the BRCA1 gene in sporadic breast tumors

Germline mutations in two major susceptibility genes BRCA1 and BRCA2 contribute to the majority of inherited breast and ovarian cancers. Besides the germline mutation, tumor progression depends on the loss of a wild-type allele. Allelic losses in the BRCA1 and BRCA2 loci have also been detected in a high proportion of sporadic breast tumors, suggesting the role of these genes in the development of non-inherited breast cancer. Forty unselected breast tumors were analyzed for the loss of heterozygosity (LOH) at BRCA1 and BRCA2 regions and tumors with allelic deletions were screened for the presence of acquired genetic alterations in respective genes. 21.1% of 38 informative tumor samples carried LOH at the BRCA1 locus whereas 33.3% of 39 informative samples showed LOH at the BRCA2 locus. Pathogenic truncating mutations in the BRCA1 gene were found in two tumor samples with allelic losses, whereas no mutations were identified in the BRCA2 gene. Mutations were not detected in non-tumor samples from the same individuals, which indicated that the BRCA1 allele was inactivated by somatic mutations in tumor tissue. The c.1116G>A (1235G>A) nonsense mutation (p.W372X) belongs to the genetic abnormalities detected infrequently in hereditary tumors; the c.3862delG (3981delG) frameshift mutation (p.E1288fsX1306) is a novel gene alteration. The occurrence of inactivating somatic mutations in sporadic breast tumors suggested the role of the BRCA1 gene in tumorigenesis in at least a minor group of patients with non-familial breast cancer.     

Prevalence of BRCA1 gene mutation in breast cancer patients in Guangxi,China

Objective: The prevalence of breast cancer susceptibility gene 1 mutation in breast cancer patients of south China has not been well revealed. This study was to invest the prevalence of BRCA1 gene mutation in breast cancer patients in Guangxi, China, and to try reflecting its relevance in genetic counseling of breast cancer. Methods: In this study, 463 breast cancer patients and 30 healthy women (control group) were involved. Entire sequence and splicing sites of BRCA1 genes were detected by PCR-DNA sequencing. Results: About 8.9% (41/463) patients were with 22 BRCA1 mutations (all in exon 10). The average hospitalized age of BRCA1-associated breast cancer cases was significantly younger (t = -2.965, P = 0.003). The nuclear grade (U = 2321.0, P = 0.030), ER (U = 4343.5, P = 0.041) and CerbB-2 (U = 3894.0, P = 0.038) expression levels, and triple negative breast cancer diagnosing rate (χ² = 4.719, P = 0.03) were disclosed more in BRCA1-associated patients. Conclusions: The four most frequent BRCA1 mutation (2798 T > C, 3971 G > A, 3971 G > A and 624 C > T) found in female breast cancer cases in Guangxi are all located in exon 10. BRCA1-associated breast cancer cases have earlier onset age, higher nuclear grade and negative ER and CerbB-2 expression.