Low frequency of BRCA1 germline mutations in 45 German breast/ovarian cancer families

BRCA1 mutation spectrum, functions, and therapeutic strategies: The story so far

BRCA1 gene mutations account for about 25-28% of hereditary Breast Cancer as BRCA1 is included in the category of high penetrance genes. Except for few commonmutations, there is a heterogenous spectrum of BRCA1 mutations in various ethnic groups. 185AGdel and 5382ins Care the most common BRCA1 alterations (founder mutations) which have been identified in most of the population. This review has been compiled with an aim to consolidate the information on genetic variants reported in BRCA1 found in various ethnic groups, their functional implications if known; involvement of BRCA1 in various cellular pathways/processes and potential BRCA1 targeted therapies. The pathological variations of BRCA1 vary among different ethical groups. A systematic search in PubMed and Google scholar for the literature on BRCA1 gene was carried out to figure out structure and function of BRCA1 gene. BRCA1 is a large protein having 1863 amino acids with multiple functional domains and interacts with multiple proteins to carry out various crucial cellular processes. BRCA1 plays a major role in maintaining genome integrity, transcription regulation, chromatin remodeling, cell cycle checkpoint control, DNA damage repair, chromosomal segregation, and apoptosis. Studies investigating the phenotypic response of mutant BRCA1 protein and comparing it to wildtype BRCA1 protein are clinically important as they are involved in homologous recombination and other repair mechanisms. These studies may help in developing more targetted therapies, detecting novel interacting partners, identification of new signaling pathways that BRCA1 is a part of or downstream target genes that BRCA1 affects.

A comprehensive focus on global spectrum of BRCA1 and BRCA2 mutations in breast cancer

Breast cancer (BC) is the most common cancer of women all over the world. BRCA1 and BRCA2 gene mutations comprise the most important genetic susceptibility of BC. Except for few common mutations, the spectrum of BRCA1 and BRCA2 mutations is heterogeneous in diverse populations. 185AGdel and 5382insC are the most important BRCA1 and BRCA2 alterations which have been encountered in most of the populations. After those Ashkenazi founder mutations, 300T>G also demonstrated sparse frequency in African American and European populations. This review affords quick access to the most frequent alterations among various populations which could be helpful in BRCA screening programs.

Five recurrent BRCA1/2 mutations are responsible for cancer predisposition in the majority of Slovenian breast cancer families

BACKGROUND

Both recurrent and population specific mutations have been found in different areas of the world and more specifically in ethnically defined or isolated populations. The population of Slovenia has over several centuries undergone limited mixing with surrounding populations. The current study was aimed at establishing the mutation spectrum of BRCA1/2 in the Slovenian breast/ovarian cancer families taking advantage of a complete cancer registration database. A second objective was to determine the cancer phenotype of these families.

METHODS

The original population database was composed of cancer patients from the Institute of Oncology Ljubljana in Slovenia which also includes current follow-up status on these patients. The inclusion criteria for the BRCA1/2 screening were: (i) probands with at least two first degree relatives with breast and ovarian cancer; (ii) probands with only two first degree relatives of breast cancer where one must be diagnosed less than 50 years of age; and (iii) individual patients with breast and ovarian cancer, bilateral breast cancer, breast cancer diagnosed before the age of 40 and male breast cancer without any other cancer in the family.

RESULTS

Probands from 150 different families met the inclusion criteria for mutation analysis of which 145 consented to testing. A BRCA1/2 mutation was found in 56 (39%). Two novel large deletions covering consecutive exons of BRCA1 were found. Five highly recurrent specific mutations were identified (1806C>T, 300T>G, 300T>A, 5382insC in the BRCA1 gene and IVS16-2A>G in the BRCA2 gene). The IVS16-2A>G in the BRCA2 gene appears to be a unique founder mutation in the Slovenian population. A practical implication is that only 4 PCR fragments can be used in a first screen and reveal the cancer predisposing mutation in 67% of the BRCA1/2 positive families. We also observed an exceptionally high frequency of 4 different pathogenic missense mutations, all affecting one of the cryptic cysteine residues of the BRCA1 Ring Finger domain.

CONCLUSION

A high mutation detection rate and the frequent occurrence of a limited array of recurring mutations facilitate BRCA1/2 mutation screening in Slovenian families.

Intronic TP53 Germline Sequence Variants Modify the Risk in German Breast/Ovarian Cancer Families

To establish the contribution of TP53 germline mutations to familial breast/ovarian cancer in Germany we screened the complete coding region of the TP53 gene in a series of German breast/ovarian cancer families negative for mutations in the BRCA1 and BRCA2 genes.Two different intronic TP53 sequence variants were identified in 6/48 (12.5%) breast/ovarian cancer families. A novel A to T nucleotide change at position 17708 in intron 10 segregating with the disease was detected in three breast cancer families (6.2%). One 17708 A>T-associated breast tumour showed loss of the wild-type allele. This variant was also found in 5/112 (4.5%) healthy controls indicating that it is a polymorphism. A second sequence variant changing a G to C at position 13964 in intron 6 not segregating with the disease was found in two breast cancer families and one breast-ovarian cancer family (6.2%). This variant has previously been shown to occur at an elevated frequency in hereditary breast cancer patients from North America and to be of functional importance leading to inhibition of apoptosis and prolongation of cell survival after DNA-damage. Screening of 185 consecutive unselected German breast cancer patients revealed the 13964 G>C variant in four patients (2.2%). Immunohistochemical analysis of the TP53 protein showed negative immunoreactivity in normal and tumour tissues of one 17708 A>T and six 13964 G>C carriers. TP53 overexpression was detected in the tumour tissue of one sporadic breast cancer patient carrying the 13964 G>C variant. Our results show that intronic changes of the TP53 gene may act as or be associated with risk modifiers in familial breast cancer.

Similar contributions of BRCA1 and BRCA2 germline mutations to early-onset breast cancer in Germany

This study was undertaken to investigate the prevalence of BRCA1 and BRCA2 germline mutations in 91 German patients unselected for family history, who were diagnosed with breast cancer before the age of 41 years. Clinical information and blood samples were obtained from all patients. A comprehensive BRCA1 and BRCA2 mutational analysis was performed using the protein truncation assay and single-strand conformational polymorphism analysis followed by DNA sequencing of variant signals detected by these assays. Five different deleterious germline mutations including four frameshift mutations and one missense mutation were identified, three in BRCA1 (3.3%) and two mutations (2.2%) in BRCA2. Both BRCA2 mutations are novel and might be specific for the German population. An additional BRCA1 missense mutation previously described and classified as an unknown variant was found. This mutation was also detected in two breast cancer patients of family P 328 and not in 140 healthy controls suggesting that it is disease associated. In addition, one common polymorphism and five novel intronic sequence variants with unknown significance were found. Our findings show that mutations in BRCA1 and BRCA2 may contribute similarly to early-onset breast cancer in Germany. Given current constraints on health-care resources, these results support the notion that BRCA1 and BRCA2 mutation screening may have the strongest impact on health-care when targeted to high-risk populations.

Molecular screening for hereditary nonpolyposis colorectal cancer: a prospective, population-based study

PURPOSE

Germline mutations in mismatch repair genes predispose to hereditary nonpolyposis colorectal cancer (HNPCC). To address effective screening programs, the true incidence of the disease must be known. Previous clinical investigations reported estimates ranging between 0.5% and 13% of all the colorectal cancer (CRC) cases, whereas biomolecular studies in Finland found an incidence of 2% to 2.7% of mutation carriers for the disease. The aim of the present report is to establish the frequency of the disease in a high-incidence area for colon cancer.

PATIENTS AND METHODS

Through the data of the local CRC registry, we prospectively collected all cases of CRC from January 1, 1996, through December 31, 1997 (N = 391). Three hundred thirty-six CRC cases (85.9% of the incident cases) were screened for microsatellite instability (MSI) with six to 12 mono- and dinucleotide markers. MSI cases were subjected to MSH2 and MLH1 germline mutation analysis and immunohistochemistry; the methylation of the promoter region was studied for MLH1.

RESULTS

Twenty-eight cases (8.3% of the total) showed MSI. MSI cases differed significantly from microsatellite-stable (MSS) cases for their proximal location (P <.01), high mucinous component (P <.01), and poor differentiation (P =.002). Of MSI cases studied (n = 12), only one with a family history compatible with HNPCC had a germline mutation (in MSH2). Five other patients with a family history of HNPCC (two with MSI and three with MSS tumors) did not show germline mutations.

CONCLUSION

We conclude that the incidence of molecularly confirmed HNPCC (one [0.3%] of 336) in a high-incidence area for CRC is lower than in previous biomolecular and clinical estimates.

Characteristics of BRCA1 mutations in a population-based case series of breast and ovarian cancer

Breast and ovarian cancers account for approximately 210000 newly diagnosed cases per year. More than half a million American women are estimated to be carriers of a breast cancer susceptibility gene. The purpose of this study was to assess the association of characteristics such as, age at diagnosis, race/ethnicity and family history of cancer with inherited BRCA1 mutations in a population-based sample of breast and ovarian cancer cases. No selection was made by race, age at diagnosis or positive family history of breast or ovarian cancer. The population under study was all breast cancer cases diagnosed in Orange County, CA, during the 1-year period beginning 1 March 1994 and all ovarian cancer cases diagnosed in Orange County during the 2-year period beginning 1 March 1994. This report focuses on the first consecutively ascertained 802 participating probands enrolled in the study, of which 9 were male breast cancer probands, 673 were female breast cancer probands and 120 were ovarian cancer probands. We observed 11 BRCA1 mutations or 1.6% (95% CI: 0.8-2.9) among the 673 female breast cancer probands and 4 BRCA1 mutations or 3.3% (95% CI: 0.8-8. 3) among the 120 ovarian cancer probands. No BRCA1 mutations were identified among the 98 non-white breast and ovarian cancer probands. The prevalence of BRCA1 mutations in non-Hispanic-white breast cancer cases below the age of 50 years was 2%. Positive family history of breast or ovarian cancers was significantly associated with BRCA1 mutation status among breast cancer probands. Similarly, positive family history of breast or ovarian cancer was significantly associated with BRCA1 mutation status among the ovarian cancer probands. In summary, we present results on the prevalence of BRCA1 mutations in a significantly larger sample of population-based breast and ovarian cancer cases than previously reported. The results indicate that, using a conservative approach to targeted genotyping of BRCA1, the frequency of mutations was consistent with those reported using similar methods of population-based case ascertainment.

Survival and tumor characteristics of German hereditary breast cancer patients

Reports from different countries have been inconclusive in attempting to relate the BRCA1 mutation status to the survival of breast cancer patients. The purpose of this study was to investigate overall and disease-free survival for German hereditary breast cancer patients. Data on clinical outcome and data on age at diagnosis of breast cancer, histology, tumor size, lymph node status, histological grade, and laterality of 36 breast cancer patients from 12 families with a BRCA1 mutation and from one family with strong evidence for linkage to BRCA1 were compared with those of 49 hereditary breast cancer patients from 23 families that did not harbor a BRCA1 mutation. Overall and disease-free survival was estimated for both groups. BRCA1 mutation carriers had a significantly earlier age of diagnosis than non-carriers (p = 0.0001) and more frequently developed contralateral breast cancer (p = 0.04). Also, BRCA1-associated tumors more frequently were of larger size (p = 0.041) and higher grade of malignancy (p = 0.005) than non-BRCA1-associated tumors. Whereas no difference in overall survival was seen, disease-free survival at 10 years differed significantly with 53.3% for BRCA1 mutation carriers and 76% for non-carriers (p = 0.02). However, after stratification for age and in multivariate analysis for mutation status, age, and bilaterality, it was shown that the worse prognosis for BRCA1 mutation carriers disappeared. Our results suggest that the worse prognosis of BRCA1 mutation carriers in terms of disease-free survival may in large part be due to the age of onset of breast cancer in this population. Thus, BRCA1 mutation status does not appear to be an independent prognostic factor.

High frequency of BRCA1/2 germline mutations in 42 Belgian families with a small number of symptomatic subjects

AIM

The initial risk assessments for BRCA1/2 mutation carriers and estimates of carrier frequencies were based on extended pedigrees with a large number of symptomatic subjects. When counselling based on BRCA gene mutation analysis was initiated, we faced requests for counselling mostly from members of small families with only two or three affected members. We report on the likelihood of finding a BRCA mutation in such small families.

METHODS

In the first 100 families that came for oncogenetic counselling since September 1994, a BRCA1/2 gene mutation screen was initiated if there were two or more symptomatic first degree relatives, if one of them had ovarian cancer, or if one breast cancer was diagnosed before the age of 50 years.

RESULTS

BRCA gene mutations were found and confirmed by sequencing in 14 out of 42 families (33%); 10 mutations were in the BRCA1 gene and four in the BRCA2 gene. Our findings indicate an increased probability of detecting a BRCA gene mutation when ovarian cancer occurred in the family. There is no increased probability of detecting a mutation with increasing numbers of breast cancers. Only 22% of the eligible presymptomatic family members opted for testing. The presymptomatic female carriers currently prefer breast surveillance rather than prophylactic surgery.

CONCLUSION

BRCA1/2 gene mutation testing can be done with reasonable efficiency in the Belgian population when there are two symptomatic family members. The availability of testing does not lead to a high frequency of requests for testing by presymptomatic family members.