title: Epigenome-wide association study reveals decreased average methylation levels years before breast cancer diagnosis.
abstract: BACKGROUND
  Interest in the potential of DNA methylation in peripheral blood as a biomarker of cancer risk is increasing. We aimed to assess whether epigenome-wide DNA methylation measured in peripheral blood samples obtained before onset of the disease is associated with increased risk of breast cancer. We report on three independent prospective nested case-control studies from the European Prospective Investigation into Cancer and Nutrition (EPIC-Italy; n = 162 matched case-control pairs), the Norwegian Women and Cancer study (NOWAC; n = 168 matched pairs), and the Breakthrough Generations Study (BGS; n = 548 matched pairs). We used the Illumina 450k array to measure methylation in the EPIC and NOWAC cohorts. Whole-genome bisulphite sequencing (WGBS) was performed on the BGS cohort using pooled DNA samples, combined to reach 50× coverage across ~16 million CpG sites in the genome including 450k array CpG sites. Mean β values over all probes were calculated as a measurement for epigenome-wide methylation.
  
  
  RESULTS
  In EPIC, we found that high epigenome-wide methylation was associated with lower risk of breast cancer (odds ratio (OR) per 1 SD = 0.61, 95 % confidence interval (CI) 0.47-0.80; -0.2 % average difference in epigenome-wide methylation for cases and controls). Specifically, this was observed in gene bodies (OR = 0.51, 95 % CI 0.38-0.69) but not in gene promoters (OR = 0.92, 95 % CI 0.64-1.32). The association was not replicated in NOWAC (OR = 1.03 95 % CI 0.81-1.30). The reasons for heterogeneity across studies are unclear. However, data from the BGS cohort was consistent with epigenome-wide hypomethylation in breast cancer cases across the overlapping 450k probe sites (difference in average epigenome-wide methylation in case and control DNA pools = -0.2 %).
  
  
  CONCLUSIONS
  We conclude that epigenome-wide hypomethylation of DNA from pre-diagnostic blood samples may be predictive of breast cancer risk and may thus be useful as a clinical biomarker.
authors.affiliation: MRC-PHE Centre for Environment and Health, Imperial College London, London, W2 1PG UK.|HuGeF Foundation, 52, Via Nizza, Torino, 10126 Italy.
authors.forename: Karin
authors.initials: K
authors.lastname: van Veldhoven
authors.affiliation: HuGeF Foundation, 52, Via Nizza, Torino, 10126 Italy.
authors.forename: Silvia
authors.initials: S
authors.lastname: Polidoro
authors.affiliation: HuGeF Foundation, 52, Via Nizza, Torino, 10126 Italy.
authors.forename: Laura
authors.initials: L
authors.lastname: Baglietto
authors.affiliation: HuGeF Foundation, 52, Via Nizza, Torino, 10126 Italy.
authors.forename: Gianluca
authors.initials: G
authors.lastname: Severi
authors.affiliation: HuGeF Foundation, 52, Via Nizza, Torino, 10126 Italy.
authors.forename: Carlotta
authors.initials: C
authors.lastname: Sacerdote
authors.affiliation: Departimento di Medicina Clinica e Chirurgia, Federico II University, Naples, Italy.
authors.forename: Salvatore
authors.initials: S
authors.lastname: Panico
authors.affiliation: Departimento di Medicina Clinica e Chirurgia, Federico II University, Naples, Italy.
authors.forename: Amalia
authors.initials: A
authors.lastname: Mattiello
authors.affiliation: Molecular and Nutritional Epidemiology Unit, Cancer Research and Prevention Institute-ISPO, Florence, Italy.
authors.forename: Domenico
authors.initials: D
authors.lastname: Palli
authors.affiliation: Molecular and Nutritional Epidemiology Unit, Cancer Research and Prevention Institute-ISPO, Florence, Italy.
authors.forename: Giovanna
authors.initials: G
authors.lastname: Masala
authors.affiliation: Epidemiology and Prevention Unit Fondazione IRCCS Istituto Nazionale dei Tumori, Milan, Italy.
authors.forename: Vittorio
authors.initials: V
authors.lastname: Krogh
authors.affiliation: Epidemiology and Prevention Unit Fondazione IRCCS Istituto Nazionale dei Tumori, Milan, Italy.
authors.forename: Claudia
authors.initials: C
authors.lastname: Agnoli
authors.affiliation: Cancer Registry ASP, Ragusa, Italy.
authors.forename: Rosario
authors.initials: R
authors.lastname: Tumino
authors.affiliation: Cancer Registry ASP, Ragusa, Italy.
authors.forename: Graziella
authors.initials: G
authors.lastname: Frasca
authors.affiliation: Epigenetics Unit, Division of Cancer, Department of Surgery and Cancer, Faculty of Medicine, Imperial College London, 4th Floor IRDB, Hammersmith Campus, Du Cane Road, London, W12 0NN UK.
authors.forename: Kirsty
authors.initials: K
authors.lastname: Flower
authors.affiliation: Epigenetics Unit, Division of Cancer, Department of Surgery and Cancer, Faculty of Medicine, Imperial College London, 4th Floor IRDB, Hammersmith Campus, Du Cane Road, London, W12 0NN UK.
authors.forename: Ed
authors.initials: E
authors.lastname: Curry
authors.affiliation: Division of Breast Cancer Research, The Institute of Cancer Research, London, UK.
authors.forename: Nicholas
authors.initials: N
authors.lastname: Orr
authors.affiliation: Division of Breast Cancer Research, The Institute of Cancer Research, London, UK.
authors.forename: Katarzyna
authors.initials: K
authors.lastname: Tomczyk
authors.affiliation: Division of Genetics and Epidemiology, The Institute of Cancer Research, London, UK.
authors.forename: Michael E
authors.initials: ME
authors.lastname: Jones
authors.affiliation: Breakthrough Breast Cancer Research Centre, The Institute of Cancer Research, London, UK.
authors.forename: Alan
authors.initials: A
authors.lastname: Ashworth
authors.affiliation: Division of Breast Cancer Research, The Institute of Cancer Research, London, UK.|Division of Genetics and Epidemiology, The Institute of Cancer Research, London, UK.
authors.forename: Anthony
authors.initials: A
authors.lastname: Swerdlow
authors.affiliation: MRC-PHE Centre for Environment and Health, Imperial College London, London, W2 1PG UK.
authors.forename: Marc
authors.initials: M
authors.lastname: Chadeau-Hyam
authors.affiliation: Department of Community Medicine, UiT-the Arctic University of Norway, Tromsø, Norway.
authors.forename: Eiliv
authors.initials: E
authors.lastname: Lund
authors.affiliation: Breakthrough Breast Cancer Research Centre, The Institute of Cancer Research, London, UK.|Division of Genetics and Epidemiology, The Institute of Cancer Research, London, UK.
authors.forename: Montserrat
authors.initials: M
authors.lastname: Garcia-Closas
authors.affiliation: Department of Community Medicine, UiT-the Arctic University of Norway, Tromsø, Norway.
authors.forename: Torkjel M
authors.initials: TM
authors.lastname: Sandanger
authors.affiliation: Epigenetics Unit, Division of Cancer, Department of Surgery and Cancer, Faculty of Medicine, Imperial College London, 4th Floor IRDB, Hammersmith Campus, Du Cane Road, London, W12 0NN UK.
authors.forename: James M
authors.initials: JM
authors.lastname: Flanagan
authors.affiliation: MRC-PHE Centre for Environment and Health, Imperial College London, London, W2 1PG UK.|HuGeF Foundation, 52, Via Nizza, Torino, 10126 Italy.
authors.forename: Paolo
authors.initials: P
authors.lastname: Vineis
keywords: Biomarker; Breast cancer; EWAS; Methylation; Peripheral blood; Risk