Gillian Ross

Genome-wide association study identifies five new breast cancer susceptibility loci

Breast cancer is the most common cancer in women in developed countries. To identify common breast cancer susceptibility alleles, we conducted a genome-wide association study in which 582,886 SNPs were genotyped in 3,659 cases with a family history of the disease and 4,897 controls. Promising associations were evaluated in a second stage, comprising 12,576 cases and 12,223 controls. We identified five new susceptibility loci, on chromosomes 9, 10 and 11 (P = 4.6 × 10−7 to P = 3.2 × 10−15). We also identified SNPs in the 6q25.1 (rs3757318, P = 2.9 × 10−6), 8q24 (rs1562430, P = 5.8 × 10−7) and LSP1 (rs909116, P = 7.3 × 10−7) regions that showed more significant association with risk than those reported previously. Previously identified breast cancer susceptibility loci were also found to show larger effect sizes in this study of familial breast cancer cases than in previous population-based studies, consistent with polygenic susceptibility to the disease.

Tumorigenesis and a DNA repair defect in mice with a truncating Brca2 mutation

Germline mutation of the BRCA2 gene carries a high risk of developing breast cancer. To study the function of this gene, we generated a mutation in Brca2 in mice. Unlike other mutations in the Brca2 gene, which are lethal early in embryogenesis when homozygous, some of our homozygous mutant mice survive to adulthood. These animals have a wide range of defects, including small size, improper differentiation of tissues, absence of germ cells and the development of lethal thymic lymphomas. Fibroblasts cultured from Brca2 −/−embryos have a defect in proliferation that may be mediated by over-expression of p53 and p21waf1/Clp1. We show that Brca2 is required for efficient DNA repair, and our results suggest that loss of the p53 checkpoint may be essential for tumour progression triggered by mutations in BRCA2.

Mutation in Brca2 stimulates error-prone homology-directed repair of DNA double-strand breaks occurring between repeated sequences.

Mutation of BRCA2 causes familial early onset breast and ovarian cancer. BRCA2 has been suggested to be important for the maintenance of genome integrity and to have a role in DNA repair by homology‐ directed double‐strand break (DSB) repair. By studying the repair of a specific induced chromosomal DSB we show that loss of Brca2 leads to a substantial increase in error‐prone repair by homology‐directed single‐strand annealing and a reduction in DSB repair by conservative gene conversion. These data demonstrate that loss of Brca2 causes misrepair of chromosomal DSBs occurring between repeated sequences by stimulating use of an error‐prone homologous recombination pathway. Furthermore, loss of Brca2 causes a large increase in genome‐wide error‐prone repair of both spontaneous DNA damage and mitomycin C‐induced DNA cross‐links at the expense of error‐free repair by sister chromatid recombination. This provides insight into the mechanisms that induce genome instability in tumour cells lacking BRCA2.

Novel Breast Cancer Susceptibility Locus at 9q31.2: Results of a Genome-Wide Association Study

BACKGROUND Genome-wide association studies have identified several common genetic variants associated with breast cancer risk. It is likely, however, that a substantial proportion of such loci have not yet been discovered. METHODS We compared 296,114 tagging single-nucleotide polymorphisms in 1694 breast cancer case subjects (92% with two primary cancers or at least two affected first-degree relatives) and 2365 control subjects, with validation in three independent series totaling 11,880 case subjects and 12,487 control subjects. Odds ratios (ORs) and associated 95% confidence intervals (CIs) in each stage and all stages combined were calculated using unconditional logistic regression. Heterogeneity was evaluated with Cochran Q and I(2) statistics. All statistical tests were two-sided. RESULTS We identified a novel risk locus for breast cancer at 9q31.2 (rs865686: OR = 0.89, 95% CI = 0.85 to 0.92, P = 1.75 × 10(-10)). This single-nucleotide polymorphism maps to a gene desert, the nearest genes being Kruppel-like factor 4 (KLF4, 636 kb centromeric), RAD23 homolog B (RAD23B, 794 kb centromeric), and actin-like 7A (ACTL7A, 736 kb telomeric). We also identified two variants (rs3734805 and rs9383938) mapping to 6q25.1 estrogen receptor 1 (ESR1), which were associated with breast cancer in subjects of northern European ancestry (rs3734805: OR = 1.19, 95% CI = 1.11 to 1.27, P = 1.35 × 10(-7); rs9383938: OR = 1.18, 95% CI = 1.11 to 1.26, P = 1.41 × 10(-7)). A variant mapping to 10q26.13, approximately 300 kb telomeric to the established risk locus within the second intron of FGFR2, was also associated with breast cancer risk, although not at genome-wide statistical significance (rs10510102: OR = 1.12, 95% CI = 1.07 to 1.17, P = 1.58 × 10(-6)). CONCLUSIONS These findings provide further evidence on the role of genetic variation in the etiology of breast cancer. Fine mapping will be needed to identify causal variants and to determine their functional effects.

BRCA1 testing should be offered to individuals with triple-negative breast cancer diagnosed below 50 years

Background:Triple-negative (TN) tumours are the predominant breast cancer subtype in BRCA1 mutation carriers. Recently, it was proposed that all individuals below 50 years of age with TN breast cancer should be offered BRCA testing. We have evaluated the BRCA1 mutation frequency and the implications for clinical practice of undertaking genetic testing in women with TN breast cancer.Methods:We undertook BRCA1 mutation analysis in 308 individuals with TN breast cancer, 159 individuals from unselected series of breast cancer and 149 individuals from series ascertained on the basis of young age and/or family history.Results:BRCA1 mutations were present in 45 out of 308 individuals. Individuals with TN cancer <50 years had >10% likelihood of carrying a BRCA1 mutation in both the unselected (11 out of 58, 19%) and selected (26 out of 111, 23%) series. However, over a third would not have been offered testing using existing criteria. We estimate that testing all individuals with TN breast cancer <50 years would generate an extra 1200 tests annually in England.Conclusion:Women with TN breast cancer diagnosed below 50 years have >10% likelihood of carrying a BRCA1 mutation and are therefore eligible for testing in most centres. However, implementation may place short-term logistical and financial burdens on genetic services.

Disruption of Brca2 increases the spontaneous mutation rate in vivo: synergism with ionizing radiation

The breast cancer predisposition gene BRCA2 encodes a protein involved in the repair of DNA double‐strand breaks, which arise spontaneously and following exposure to ionizing radiation (IR). To develop a mouse model that examines the effect of BRCA2 mutation and IR exposure on in vivo somatic mutation acquisition, we crossed mice with targeted disruption of Brca2 with a LacZ transgenic mutation reporter strain. Loss of both wild‐type Brca2 alleles caused a 2.3‐fold increase, equivalent to an extra 100 mutations per cell, in the in vivo acquisition of spontaneous somatic mutation by 2 weeks gestation. IR (4 Gy) had a disproportionate effect on animals homozygous for Brca2 disruption, inducing 3.4‐fold more mutations compared with wild‐type animals. These data provide the first evidence that loss of Brca2 increases in vivo somatic mutation acquisition and synergizes with IR exposure, with potential attendant implications for mammographic screening and therapeutic IR in mutation carriers.

Breast cancer in women after treatment for Hodgkin's disease

Although substantial progress has been made in the management of Hodgkins lymphoma during the past 30 years, the development of secondary malignant diseases has emerged as a serious consequence of treatment. In particular, extended follow-up of patients with Hodgkins disease has revealed an increased risk of breast cancer. We have systematically reviewed all published literature on breast cancer after treatment for Hodgkins disease and show that high risk is particularly associated with treatment at a young age, mantle radiotherapy, and chemotherapy. Breast cancers in this context differ from sporadic disease because they develop in younger women, are associated with a high incidence of bilateral disease, and are generally located near the midline of the body. The risk of breast cancer is lower in patients who receive newer, combined modality treatments for Hodgkins disease. In this review we discuss a protocol for formal follow-up and screening of patients who have recovered from Hodgkins disease to aid early diagnosis and ensure the possibility of effective management.

Variation in the manganese superoxide dismutase gene (SOD2) is not a major cause of radiotherapy complications in breast cancer patients

BACKGROUND AND PURPOSE Small proportions of patients receiving radiotherapy develop marked long-term radiation damage. It is thought that this is due, at least in part, to intrinsic differences in cellular radiosensitivity, but the underlying mechanism is unknown. Reactive oxygen species are involved in cellular radiation damage, hence inter-individual differences in free radical detoxification may be related to radiosensitivity. Within mitochondria manganese superoxide dismutase (MnSOD) provides a major defence against oxidative damage by reactive oxygen species. MnSOD has been linked to expression of malignant phenotype and apoptosis and polymorphic variation in the gene, SOD2 to risk of breast cancer. MATERIALS AND METHODS Forty-one breast cancer patients developing marked changes in breast appearance after radiotherapy and 39 patients who showed no clinically detectable reaction after radiotherapy were analyzed for germline sequence variation in SOD2. RESULTS The Ala-9Val polymorphism was detected, but no other sequence variants were detected in SOD2. Both alleles of the Ala-9Val polymorphism were equally distributed between the two patient groups. CONCLUSIONS Sequence variation in SOD2 is not the major cause of radiotherapy complications in women with breast cancer.

CYP3A Variation, Premenopausal Estrone Levels, and Breast Cancer Risk

BACKGROUND Epidemiological studies have provided strong evidence for a role of endogenous sex steroids in the etiology of breast cancer. Our aim was to identify common variants in genes involved in sex steroid synthesis or metabolism that are associated with hormone levels and the risk of breast cancer in premenopausal women. METHODS We measured urinary levels of estrone glucuronide (E1G) using a protocol specifically developed to account for cyclic variation in hormone levels during the menstrual cycle in 729 healthy premenopausal women. We genotyped 642 single-nucleotide polymorphisms (SNPs) in these women; a single SNP, rs10273424, was further tested for association with the risk of breast cancer using data from 10 551 breast cancer case patients and 17 535 control subjects. All statistical tests were two-sided. RESULTS rs10273424, which maps approximately 50 kb centromeric to the cytochrome P450 3A (CYP3A) gene cluster at chromosome 7q22.1, was associated with a 21.8% reduction in E1G levels (95% confidence interval [CI] = 27.8% to 15.3% reduction; P = 2.7 × 10(-9)) and a modest reduction in the risk of breast cancer in case patients who were diagnosed at or before age 50 years (odds ratio [OR] = 0.91, 95% CI = 0.83 to 0.99; P = .03) but not in those diagnosed after age 50 years (OR = 1.01, 95% CI = 0.93 to 1.10; P = .82). CONCLUSIONS Genetic variation in noncoding sequences flanking the CYP3A locus contributes to variance in premenopausal E1G levels and is associated with the risk of breast cancer in younger patients. This association may have wider implications given that the most predominantly expressed CYP3A gene, CYP3A4, is responsible for metabolism of endogenous and exogenous hormones and hormonal agents used in the treatment of breast cancer.

HER2 significance and treatment outcomes after radiotherapy for brain metastases in breast cancer patients

The aim of this retrospective study was to examine the influence of HER2 status on outcome in breast cancer patients following whole brain radiotherapy (WBRT) for cerebral metastases. One hundred and eighty one patients with recordable HER2 status, who received WBRT at single institution were identified and stratified according to HER2 status. Eighty eight were HER2 positive (HER2+) (49%) and 93 HER2 negative (HER2-) (51%). A total of 72 (82%) HER2+ group developed brain metastases whilst on chemotherapy compared with 45 (48%) in HER2- group. Median survival after WBRT was 8 months (1-38) for HER2+ patients and 4 (1-64) for HER2- patients p=0.01. On brain metastasis progression, 18 (20%) of HER2+ patients received further local therapy compared with 6 (6%) in HER2- group. This study shows superior survival in HER2+ group following WBRT as compared to HER2- group and more aggressive management on disease progression in HER2+ group.