Katarzyna Tomczyk

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.

Genome-wide association study identifies a common variant in RAD51B associated with male breast cancer risk

We conducted a genome-wide association study of male breast cancer comprising 823 cases and 2,795 controls of European ancestry, with validation in independent sample sets totaling 438 cases and 474 controls. A SNP in RAD51B at 14q24.1 was significantly associated with male breast cancer risk (P = 3.02 × 10−13; odds ratio (OR) = 1.57). We also refine association at 16q12.1 to a SNP within TOX3 (P = 3.87 × 10−15; OR = 1.50).

Temporal stability and determinants of white blood cell DNA methylation in the Breakthrough Generations Study

Background: Epigenome-wide association studies (EWAS) using measurements of blood DNA methylation are performed to identify associations of methylation changes with environmental and lifestyle exposures and disease risk. However, little is known about the variation of methylation markers in the population and their stability over time, both important factors in the design and interpretation of EWAS. We aimed to identify stable variable methylated probes (VMP), i.e., markers that are variable in the population, yet stable over time. Methods: We estimated the intraclass correlation coefficient (ICC) for each probe on the Illumina 450K methylation array in paired samples collected approximately 6 years apart from 92 participants in the Breakthrough Generations Study. We also evaluated relationships with age, reproductive and hormonal history, weight, alcohol intake, and smoking. Results: Approximately 17% of probes had an ICC > 0.50 and were considered stable VMPs (stable-VMPs). Stable-VMPs were enriched for probes located in “shores” bordering CpG islands, and at approximately 1.3 kb downstream from the transcription start site in the transition between the unmethylated promoter and methylated gene body. Both cross-sectional and longitudinal data analyses provided strong evidence for associations between changes in methylation levels and aging. Smoking-related probes at 2q37.1 and AHRR were stable-VMPs and related to time since quitting. We also observed associations between methylation and weight changes. Conclusion: Our results provide support for the use of white blood cell DNA methylation as a biomarker of exposure in EWAS. Impact: Larger studies, preferably with repeated measures over time, will be required to establish associations between specific probes and exposures. Cancer Epidemiol Biomarkers Prev; 24(1); 221–9. ©2014 AACR.

Genetic Variants at Chromosomes 2q35, 5p12, 6q25.1, 10q26.13, and 16q12.1 Influence the Risk of Breast Cancer in Men

Male breast cancer accounts for approximately 1% of all breast cancer. To date, risk factors for male breast cancer are poorly defined, but certain risk factors and genetic features appear common to both male and female breast cancer. Genome-wide association studies (GWAS) have recently identified common single nucleotide polymorphisms (SNPs) that influence female breast cancer risk; 12 of these have been independently replicated. To examine if these variants contribute to male breast cancer risk, we genotyped 433 male breast cancer cases and 1,569 controls. Five SNPs showed a statistically significant association with male breast cancer: rs13387042 (2q35) (odds ratio (OR)  = 1.30, p = 7.98×10−4), rs10941679 (5p12) (OR = 1.26, p = 0.007), rs9383938 (6q25.1) (OR = 1.39, p = 0.004), rs2981579 (FGFR2) (OR = 1.18, p = 0.03), and rs3803662 (TOX3) (OR = 1.48, p = 4.04×10−6). Comparing the ORs for male breast cancer with the published ORs for female breast cancer, three SNPs—rs13387042 (2q35), rs3803662 (TOX3), and rs6504950 (COX11)—showed significant differences in ORs (p<0.05) between sexes. Breast cancer is a heterogeneous disease; the relative risks associated with loci identified to date show subtype and, based on these data, gender specificity. Additional studies of well-defined patient subgroups could provide further insight into the biological basis of breast cancer development.

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.

Mitochondrial DNA Copy Number in Peripheral Blood Cells and Risk of Developing Breast Cancer

Increased mitochondrial DNA (mtDNA) copy number in peripheral blood cells (PBC) has been associated with the risk of developing several tumor types. Here we evaluate sources of variation of this biomarker and its association with breast cancer risk in a prospective cohort study. mtDNA copy number was measured using quantitative real-time PCR on PBC DNA samples from participants in the UK-based Breakthrough Generations Study. Temporal and assay variation was evaluated in a serial study of 91 women, with two blood samples collected approximately 6-years apart. Then, associations with breast cancer risk factors and risk were evaluated in 1,108 cases and 1,099 controls using a nested case-control design. In the serial study, mtDNA copy number showed low assay variation but large temporal variation [assay intraclass correlation coefficient (ICC), 79.3%-87.9%; temporal ICC, 38.3%). Higher mtDNA copy number was significantly associated with younger age at blood collection, being premenopausal, having an older age at menopause, and never taking HRT, both in cases and controls. Based on measurements in a single blood sample taken on average 6 years before diagnosis, higher mtDNA copy number was associated with increased breast cancer risk [OR (95% CI) for highest versus lowest quartile, 1.37 (1.02-1.83); P trend = 0.007]. In conclusion, mtDNA copy number is associated with breast cancer risk and represents a promising biomarker for risk assessment. The relatively large temporal variation should be taken into account in future analyses.

Abstract P1-04-01: Epigenome-wide association study for breast cancer risk using whole genome and target captured bisulphite sequencing: A pooled case-control study nested in the breakthrough generations study

Background: The field of epigenetic epidemiology has rapidly advanced and recent work has discovered epigenetic markers of breast cancer risk in white blood cell (WBC) DNA. Using Epigenome-Wide Association Studies (EWAS) on the Illumina 450k methylation array, we and others have shown epigenome-wide hypomethylation (-0.2%, p -16 ) in incident breast cancer cases compared with controls in several prospective cohorts. We have proposed a mechanism that involves cancer risk exposures, lifetime and environmental events, that alter the epigenome and stably modifies an individual9s cancer risk. However, more work is needed to establish the clinical utility of this observation, the underlying causes of this variation and to determine whether the 1.7% of CpG sites targeted by the 450k array are representative of the remaining 98% of the epigenome that has not yet been interrogated. Our overall aim is to identify epigenetic traits within the epigenome that are associated with the risk of developing breast cancer. Methods: We conducted an EWAS using whole genome bisulphite sequencing (WGBS) of WBC DNA from incident breast cancer cases (n=548) compared to matched controls (n=548) from a prospective cohort (Breakthrough Generations Study) using a DNA pooling approach. Eight DNA pools were prepared in sequencing libraries and sequenced on the Hiseq2500 at PE100bp reads, resulting in ~10-fold coverage per CpG, per library, across ~20 million mappable CpG sites. Each pooled sample was also analysed in triplicate on the Illumina 450k methylation array for validation. We used Agilent target capture bisulphite sequencing (TCBS) for technical validation in a subset of breast cancer cases (n=48) and matched controls (n=48), individually barcoded and sequenced on the MiSeq at PE150bp, aiming for >1000 fold coverage of 425 kb targeted sequence. Results: Interrogation of specific genomic regions showed that gene-body methylation averages tended to be hypomethylated in cases, while CpG island averages identified both hypo- and hypermethylation. We have validated the same direction of change in 40/51 CpG islands that were covered by the Illumina 450K methylation array and have developed a target capture panel for validation of 960 gene body regions and 224 CpG island regions that were identified as significantly different between cases and controls (average -11%, FDR Conclusions: Results indicate that epigenome-wide hypomethylation and methylation in specific sites, particularly gene bodies, measured in pre-diagnostic blood samples may be predictive of breast cancer risk, and may thus be useful as a risk biomarker. Citation Format: Flanagan JM, Curry E, Stirling L, Flower K, Orr N, Tomczyk K, Coulson P, Jones M, Ashworth A, Swerdlow A, Brown R, Garcia-Closas M. Epigenome-wide association study for breast cancer risk using whole genome and target captured bisulphite sequencing: A pooled case-control study nested in the breakthrough generations study [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P1-04-01.

Abstract P3-08-04: Impact of CYP3A variation on estrone levels and breast cancer risk

Background: Epidemiological studies provide 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 were associated with premenopausal hormone levels and breast cancer risk. Methods: We measured urinary estrone glucuronide (E1G) and pregnanediol glucuronide (PG) using a protocol specifically developed to account for cyclic variation in hormone levels during the menstrual cycle, plasma sex hormone-binding globulin (SHBG) and androgenic precursors in up to 763 healthy premenopausal women. We genotyped 642 single nucleotide polymorphisms (SNPs) in these women; a single SNP was further tested for association with breast cancer risk in data from 10,551 breast cancer case patients and 17,535 control subjects. All statistical tests were two-sided. Results: rs10273424 mapping approximately 50kb centromeric to the cytochrome P450 3A (CYP3A) cluster (7q22.1) was associated with a 21.8% reduction in E1G levels (P = 2.7 × 10 −9 ) and a modest reduction in breast cancer risk in cases diagnosed at or before age 50 (OR = 0.91; P = 0.03) but not older cases (odds ratio (OR) = 1.01; P = 0.82). A rare non-synonymous SHBG SNP was associated with reduced plasma SHBG levels. Conclusions: Genetic variation in non-coding sequences flanking the CYP3A locus contributes to variance in premenopausal E1G levels and breast cancer risk in younger cases. Since CYP3A4, the most predominantly expressed CYP3A gene, is responsible for metabolism of endogenous and exogenous hormones and hormonal agents such as tamoxifen, used in the treatment of breast cancer this association may have wider implications. Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P3-08-04.