title: The integrative epigenomic-transcriptomic landscape of ER positive breast cancer.
abstract: BACKGROUND
  While recent integrative analyses of copy number and gene expression data in breast cancer have revealed a complex molecular landscape with multiple subtypes and many oncogenic/tumour suppressor driver events, much less is known about the role of DNA methylation in shaping breast cancer taxonomy and defining driver events.
  
  
  RESULTS
  Here, we applied a powerful integrative network algorithm to matched DNA methylation and RNA-Seq data for 724 estrogen receptor (ER)-positive (ER+) breast cancers and 111 normal adjacent tissue specimens from The Cancer Genome Atlas (TCGA) project, in order to identify putative epigenetic driver events and to explore the resulting molecular taxonomy. This revealed the existence of nine functionally deregulated epigenetic hotspots encompassing a total of 146 genes, which we were able to validate in independent data sets encompassing over 1000 ER+ breast cancers. Integrative clustering of the matched messenger RNA (mRNA) and DNA methylation data over these genes resulted in only two clusters, which correlated very strongly with the luminal-A and luminal B subtypes. Overall, luminal-A and luminal-B breast cancers shared the same epigenetically deregulated hotspots but with luminal-B cancers exhibiting increased aberrant DNA methylation patterns relative to normal tissue. We show that increased levels of DNA methylation and mRNA expression deviation from the normal state define a marker of poor prognosis. Our data further implicates epigenetic silencing of WNT signalling antagonists and bone morphogenetic proteins (BMP) as key events underlying both luminal subtypes but specially of luminal-B breast cancer. Finally, we show that DNA methylation changes within the identified epigenetic interactome hotspots do not exhibit mutually exclusive patterns within the same cancer sample, instead exhibiting coordinated changes within the sample.
  
  
  CONCLUSIONS
  Our results indicate that the integrative DNA methylation and transcriptomic landscape of ER+ breast cancer is surprisingly homogeneous, defining two main subtypes which strongly correlate with luminal-A/B subtype status. In particular, we identify WNT and BMP signalling as key epigenetically deregulated tumour suppressor pathways in luminal ER+ breast cancer, with increased deregulation seen in luminal-B breast cancer.
authors.affiliation: CAS Key Lab for Computational Biology, CAS-MPG Partner Institute for Computational Biology, Chinese Academy of Sciences, Shanghai Institute for Biological Sciences, 320 Yue Yang Road, 200031 Shanghai, China.
authors.forename: Yang
authors.initials: Y
authors.lastname: Gao
authors.affiliation: Department of Women's Cancer, University College London, 74 Huntley Street, London, WC1E 6BT UK.
authors.forename: Allison
authors.initials: A
authors.lastname: Jones
authors.affiliation: University Clinic Erlangen, Department of Gynaecology and Obstetrics, Friedrich-Alexander University Erlangen-Nuremberg, Erlangen, 91054 Germany.
authors.forename: Peter A
authors.initials: PA
authors.lastname: Fasching
authors.affiliation: University Clinic Erlangen, Department of Gynaecology and Obstetrics, Friedrich-Alexander University Erlangen-Nuremberg, Erlangen, 91054 Germany.
authors.forename: Matthias
authors.initials: M
authors.lastname: Ruebner
authors.affiliation: University Clinic Erlangen, Department of Gynaecology and Obstetrics, Friedrich-Alexander University Erlangen-Nuremberg, Erlangen, 91054 Germany.
authors.forename: Matthias W
authors.initials: MW
authors.lastname: Beckmann
authors.affiliation: Department of Women's Cancer, University College London, 74 Huntley Street, London, WC1E 6BT UK.
authors.forename: Martin
authors.initials: M
authors.lastname: Widschwendter
authors.affiliation: CAS Key Lab for Computational Biology, CAS-MPG Partner Institute for Computational Biology, Chinese Academy of Sciences, Shanghai Institute for Biological Sciences, 320 Yue Yang Road, 200031 Shanghai, China ; Department of Women's Cancer, University College London, 74 Huntley Street, London, WC1E 6BT UK ; Statistical Genomics Group, Paul O'Gorman Building, UCL Cancer Institute, University College London, 72 Huntley Street, London, WC1E 6BT UK.
authors.forename: Andrew E
authors.initials: AE
authors.lastname: Teschendorff