BRCA基因及其相关乳腺癌

BRCA基因是家族性乳腺癌的易感基因,已经明确的有BRCA1和BRCA2,是否存在“BRCA3”是目前研究的热点。BRCA相关乳腺癌有特殊的临床病理学特征。BRCA基因突变携带者接受预防性双侧乳腺或卵巢切除能降低乳腺癌发生风险。单纯保乳术不适用于BRCA相关乳腺癌,应该考虑行双侧乳腺切除或保乳术联合双侧卵巢切除。BRCA基因可能是某些人群的不良预后因素。     

BRCA1和BRCA2的始祖突变

BRCA1和BRCA2的突变与乳腺癌和卵巢癌的发生密切相关。BRCA1和BRCA2的始祖突变多种多样,而且在不同民族、不同地域的人口中突变类型和频率不尽相同。在特定的人口中,始祖突变由于存在始祖效应,其发生率较高。与昂贵的全基因扫描相比,始祖突变检测更加方便、经济和易于普及,能为相关癌症的预防和治疗提供信息。     

BRCA1 and BRCA2: 1994 and beyond

The discovery of the first gene associated with hereditary breast cancer, BRCA1, was anticipated to greatly increase our understanding of both hereditary and sporadic forms of breast cancer, and to lead to therapeutic and preventive breakthroughs. Much has been learned during the past decade about the genetic epidemiology of breast cancer, the ethnic distribution and clinical consequences of BRCA1 and BRCA2 mutations, and the central role of DNA repair in breast cancer susceptibility. The ability to translate this knowledge into novel treatments, however, remains elusive.     

219例中国汉族遗传性乳腺癌患者BRCA1和BRCA2突变的研究

  目的  分析中国新疆多民族地区的高风险遗传性乳腺癌BRCA1/2基因突变位点情况。  方法  以2009年1月到2010年12月新疆医科大学附属肿瘤医院收治的来自新疆地区的68例符合高风险遗传性乳腺癌标准的患者为研究对象,其中HBC 12例,HBOC 4例,E-BC 25例,BI-BC 10例,TNB 17例。通过外周静脉血提取基因组DNA,对BRCA1/2基因的全部编码序列进行扩增。用高效液相色谱分析（DHPLC）进行突变分析预筛,结果经DNA测序验证。  结果  BRCA1/2致病性突变在新疆地区高风险遗传性乳腺癌的突变率为8.8%（6/68）。其中BRCA1的突变率为4.4%（3/68）,BRCA2的突变率为4.4%（3/68）。不同民族之间BRCA1/2突变率无统计学差异。  结论  中国新疆多民族地区的高风险遗传性乳腺癌患者部分病例具有与内地汉族人群不同的BRCA基因突变谱。BRCA1 2073delA,BRCA2 6873del CTCC及BRCA2 9481del A可能是新疆遗传性乳腺癌特有的突变位点。     

BRCA1 and BRCA2 as ovarian cancer susceptibility genes

Individuals carrying germline mutations in one allele of the BRCA1 or BRCA2 genes are at significantly increased risk of developing cancer. Although the increased risk of breast cancer is often highlighted, cancer at several other sites is also considerably more common in these individuals. Here, we discuss existing knowledge of the role of BRCA1 and BRCA2 mutation in pre-disposition to ovarian cancer. The risk of an individual with a mutation developing cancer of the ovary appears to be influenced by the position of the mutation within the BRCA gene, the presence of allelic variants of modifying genes and the hormonal exposure of the carrier. Once cancer has developed, the pathology and clinical behaviour of BRCA-associated tumours is distinct from sporadic cases. Comparison of the pathogenesis of breast and ovarian cancers caused by BRCA mutation provides insight into the function of BRCA proteins as tumour suppressors in different cellular environments.     

Clinical management of BRCA1 and BRCA2 mutation carriers

The cancer susceptibility genes BRCA1 and BRCA2 appear to be responsible for virtually all hereditary breast ovarian families, and a smaller subset of hereditary site-specific breast cancer families. Fortunately, effective strategies have been developed to reduce the risk for the development of breast and ovarian cancer in women with BRCA1/2 mutations, making genetic testing for these mutations an important part of the management at women with a strong family history of these diseases. Here, we review the current evidence for risk reduction strategies and outline future research directions.     

Secondary BRCA1 and BRCA2 alterations and acquired chemoresistance

Tumor suppressor BRCA1 and BRCA2 are frequently mutated in familial breast and ovarian cancer. More than ten percent of women with breast or ovarian cancer carry BRCA1 or BRCA2 (BRCA1/2) mutations. Cancers that arise in mutation carriers have often lost the wild-type allele through somatic alterations during tumor progression. BRCA1/2 play important roles in homologous recombination repair of DNA double-strand breaks. Because of this, BRCA1/2-deficient cancers often have a better response to DNA cross-linking agents such as platinum analogues and to poly(ADP-ribose) polymerase (PARP) inhibitors. However, over time, the majority of these BRCA1/2-deficient cancers become resistant and patients die from refractory diseases. Three recent studies demonstrated that acquired resistance to platinum analogues or PARP inhibitors in tumors carrying frame-shift BRCA1/2 mutations came from restored BRCA1/2 expression and HR function due to secondary intragenic mutations that corrected the open reading frames of mutated BRCA1/2.     

Cancer treatment according to BRCA1 and BRCA2 mutations

Identification of germline mutations associated with significant cancer susceptibility has the potential to change all aspects of an individual's care, from screening to cancer treatment. For example, women with germline mutations in BRCA1 and BRCA2 have markedly elevated risks of breast and ovarian cancer and the identification of these germline mutations has led to specific screening and prevention strategies. More recently, advances in the understanding of the biological function of BRCA1 and BRCA2 have led to clinical trials testing targeted therapies in this population, particularly poly(ADP-ribose) polymerase (PARP) inhibitors. Unfortunately, the development of PARP inhibitors has not been as rapid as anticipated and has been more challenging than expected. Somatic mutations identified in many cancer types have allowed the development of therapeutics that target these mutated genes, and many of these agents obtained rapid regulatory approval and are currently in widespread clinical practice. Diagnostic testing has a central role in targeted cancer therapeutics for both somatic and germline mutations. Although the era of molecular medicine and targeted therapies has led to significant changes in the practice of oncology, new challenges continue to arise.     

BRCA1 and BRCA2 germline mutations in lymphoma patients

Mutations in the BRCA1 and BRCA2 tumor suppressor genes are associated with an increased risk for breast and ovarian cancers as well as other types of malignancies. The observation of a germline BRCA1 mutation in an index case with a lymphoid neoplasm in the setting of a family history of breast cancer prompted us to explore the role of BRCA germline mutations as lymphoma susceptibility alleles. A panel of 286 DNA samples from Jewish lymphoma patients was analyzed for the three most frequent BRCA1 and BRCA2 germline mutations in those of Ashkenazi Jewish heritage, and compared to a cohort of 5010 DNA samples from healthy controls. Of the 286 cases, 2 patients carried a germline BRCA mutation; both were diagnosed at an early age with an intermediate grade non-Hodgkin's lymphoma. This data indicate that germline BRCA mutations are not associated with an increased risk for lymphoid malignancies.     

Cancer risks among BRCA1 and BRCA2 mutation carriers

BRCA1 and BRCA2 mutations increase breast and ovarian cancer risks substantially enough to warrant risk reduction surgery, despite variable risk estimates. Underlying this variability are methodological issues, and also complex genetic and nongenetic effects. Although many modifying factors are unidentified, known factors can already be incorporated in individualised risk prediction.     

Clinical significance of large rearrangements in BRCA1 and BRCA2

BACKGROUND:

Current estimates of the contribution of large rearrangement (LR) mutations in the BRCA1 (breast cancer 1, early onset) and BRCA2 (breast cancer 2, early onset) genes responsible for hereditary breast and ovarian cancer are based on limited studies of relatively homogeneous patient populations. The prevalence of BRCA1/2 LRs was investigated in 48,456 patients with diverse clinical histories and ancestries, referred for clinical molecular testing for suspicion of hereditary breast and ovarian cancer.

METHODS:

Sanger sequencing analysis was performed for BRCA1/2 and LR testing for deletions and duplications using a quantitative multiplex polymerase chain reaction assay. Prevalence data were analyzed for patients from different risk and ethnic groups between July 2007 and April 2011. Patients were designated as “high‐risk” if their clinical history predicted a high prior probability, wherein LR testing was performed automatically in conjunction with sequencing. “Elective” patients did not meet the high‐risk criteria, but underwent LR testing as ordered by the referring health care provider.

RESULTS:

Overall BRCA1/2 mutation prevalence among high‐risk patients was 23.8% versus 8.2% for the elective group. The mutation profile for high‐risk patients was 90.1% sequencing mutations versus 9.9% LRs, and for elective patients, 94.1% sequencing versus 5.9% LRs. This difference may reflect the bias in high‐risk patients to carry mutations in BRCA1, which has a higher penetrance and frequency of LRs compared with BRCA2. There were significant differences in the prevalence and types of LRs in patients of different ancestries. LR mutations were significantly more common in Latin American/Caribbean patients.

CONCLUSIONS:

Comprehensive LR testing in conjunction with full gene sequencing is an appropriate strategy for clinical BRCA1/2 analysis. Cancer 2012. © 2012 American Cancer Society.     

Refining BRCA1 and BRCA2 penetrance estimates in the clinic

Genetic testing for mutations in BRCA1 and BRCA2 can provide important information to women and help guide clinical management decisions regarding interventions such as oophorectomy to reduce cancer risk. However, variability exists in risks of breast and ovarian cancer in individual BRCA1 and BRCA2 mutation carriers, with potential contributing factors including genotype-phenotype correlations, modifier genes, environmental and reproductive exposures, and the impact of interventions. Ultimately, the clinical goal is to provide individualized assessment of breast and ovarian cancer risk to BRCA1 and BRCA2 mutation carriers accounting for these variables to aid decision-making. This article discusses factors affecting the penetrance of cancer risks in BRCA1/2 mutation carriers.     

BRCA somatic mutations and epigenetic BRCA modifications in serous ovarian cancer

The significant activity of poly(ADP-ribose)polymerase (PARP) inhibitors in the treatment of germline BRCA mutation-associated ovarian cancer, which represents ∼15% of HGS cases, has recently led to European Medicines Agency and food and drug administration approval of olaparib. Accumulating evidence suggests that PARP inhibitors may have a wider application in the treatment of sporadic ovarian cancers. Up to 50% of HGS ovarian cancer patients may exhibit homologous recombination deficiency (HRD) through mechanisms including germline BRCA mutations, somatic BRCA mutations, and BRCA promoter methylation. In this review, we discuss the role of somatic BRCA mutations and BRCA methylation in ovarian cancer. There is accumulating evidence for routine somatic BRCA mutation testing, but the relevance of BRCA epigenetic modifications is less clear. We explore the challenges that need to be addressed if the full potential of these markers of HRD is to be utilised in clinical practice.     

Bilateral risk-reducing oophorectomy in BRCA1 and BRCA2 mutation carriers

Bilateral risk-reducing oophorectomy (BRRO) is widely used for cancer risk reduction in women with BRCA1 and BRCA2 (BRCA1/2) mutations. BRRO significantly reduces breast cancer risk by approximately 50% and ovarian cancer risk by 85% to 95%, but it may be accompanied by menopausal symptoms, impaired quality of life, and accelerated bone loss. Therefore, decisions regarding the timing of BRRO, the risks and benefits of a simultaneous hysterectomy, and the use of hormone replacement therapy (HRT) must be made in concert with the patient and individualized to their circumstances. However, recent data demonstrate that HRT after BRRO in unaffected premenopausal women does not negate the breast cancer risk reduction that BRRO provides. This article reviews the studies regarding BRRO in BRCA1/2 mutation carriers, with particular focus on the use of HRT.     

家族性乳腺癌家系成员乳腺癌易感基因突变的研究

目的研究河北省地区家族性乳腺癌家系中的患者及健康一级亲属乳腺癌易感基因1（BRCAl）和乳腺癌易感基因2（BRCA2）突变位点及携带情况。方法研究对象为2002年6月至2008年5月河北医科大学第四医院接诊的乳腺癌患者及其亲属,分别来自12个独立的汉族家族性乳腺癌家系,该家系中有2个及2个以上一级或二级亲属乳腺癌患病史,研究病例包括13例患者及46例健康一级亲属,共59例样本。由外周血提取基因组DNA,采用聚合酶链反应一单链构象多态性分析（PCR—SSCP）和基因测序技术对国内外报告中常见的4个BRCAl／BRCA2突变热点区域（BRCAl：外显子2、11、20;BRCA2外显子11）进行检测。结果发现1个BRCAl突变位点（4193insA）和1个BRCA2突变位点（5329insT）,全部为移码突变;发现4个变异位点（BRCAl：4165T〉A、287G〉C,BRCA2：6251G〉T、5416C〉A）,4193insA、5329insT、287G〉C携带者的家系中均有3例乳腺癌患者。结论BRCAl（4193insA）、BRCA2（5329insT）以及BRCAl：4165T〉A、287G〉C和BRCA2：6251G〉T、5416C〉A可能是河北省家族性乳腺癌相关性突变位点,其携带者家系中乳腺癌发病率明显升高,建议对其一级亲属密切随访或尽早进行手术或药物干预。     

家族性乳腺癌患者及家系成员乳腺癌易感基因携带情况调查

目的 乳腺癌易感基因1(breast cancer susceptibility gene 1,BRCA1)和BRCA2基因已经证实与家族性乳腺癌密切相关.本研究旨在分析中国汉族家族性乳腺癌患者及家系成员BRCA1和BRCA2突变特征及携带情况.方法 收集2013 12-02-2015-06-08军事医学科学院附属医院确诊的中国汉族家族性乳腺癌患者55例及家系成员48名,共计103例样本.柚取外周静脉血提取DNA,应用聚合酶链反应(polymerase chain reaction,PCR) DNA直接测序方法检测BRCA1和BRCA2基因全编码外显子序列.结果 55例家族性乳腺癌患者中发现5个BRCA基因致病性突变位点,1个突变位点乳腺癌信息库中见报道(BRCA1:4730insG),4个为新发现突变位点(BRCA1:1937insC,4538insAG;BRCA2:1382delA,2820delA).家族性乳腺癌患者BRCA1/2突变率为9.09％(BRCA1,5.45％;BRCA2,3.64％),其中三阴性乳腺癌患者突变率为22.22％(x2 =1.99,P=0.20),早发性乳腺癌患者(≤35岁)突变率为20.00％,x2=0.79,P=0.39.48例家系成员检测到3个新发现突变位点(BRCA1:1370insA,3459insA;BRCA2:6502insT),总突变率为6.25％.结论 中国汉族家族性乳腺癌患者BRCA基因突变率显著低于国外,应重点关注有家族史的三阴性乳腺癌患者和早发性乳腺癌患者;家系成员中发现BRCA基因致病性突变,家系成员突变率和发病风险有待进一步研究,应引起重视.