title: Claudin-low breast cancers: clinical, pathological, molecular and prognostic characterization.
abstract: BACKGROUND
  The lastly identified claudin-low (CL) subtype of breast cancer (BC) remains poorly described as compared to the other molecular subtypes. We provide a comprehensive characterization of the largest series of CL samples reported so far.
  
  
  METHODS
  From a data set of 5447 invasive BC profiled using DNA microarrays, we identified 673 CL samples (12,4%) that we describe comparatively to the other molecular subtypes at several levels: clinicopathological, genomic, transcriptional, survival, and response to chemotherapy.
  
  
  RESULTS
  CL samples display profiles different from other subtypes. For example, they differ from basal tumors regarding the hormone receptor status, with a lower frequency of triple negative (TN) tumors (52% vs 76% for basal cases). Like basal tumors, they show high genomic instability with many gains and losses. At the transcriptional level, CL tumors are the most undifferentiated tumors along the mammary epithelial hierarchy. Compared to basal tumors, they show enrichment for epithelial-to-mesenchymal transition markers, immune response genes, and cancer stem cell-like features, and higher activity of estrogen receptor (ER), progesterone receptor (PR), EGFR, SRC and TGFβ pathways, but lower activity of MYC and PI3K pathways. The 5-year disease-free survival of CL cases (67%) and the rate of pathological complete response (pCR) to primary chemotherapy (32%) are close to those of poor-prognosis and good responder subtypes (basal and ERBB2-enriched). However, the prognostic features of CL tumors are closer to those observed in the whole BC series and in the luminal A subtype, including proliferation-related gene expression signatures (GES). Immunity-related GES valuable in basal breast cancers are not significant in CL tumors. By contrast, the GES predictive for pCR in CL tumors resemble more to those of basal and HER2-enriched tumors than to those of luminal A tumors.
  
  
  CONCLUSIONS
  Many differences exist between CL and the other subtypes, notably basal. An unexpected finding concerns the relatively high numbers of ER-positive and non-TN tumors within CL subtype, suggesting a larger heterogeneity than in basal and luminal A subtypes.
authors.forename: Renaud
authors.initials: R
authors.lastname: Sabatier
authors.forename: Pascal
authors.initials: P
authors.lastname: Finetti
authors.forename: Arnaud
authors.initials: A
authors.lastname: Guille
authors.forename: José
authors.initials: J
authors.lastname: Adelaide
authors.forename: Max
authors.initials: M
authors.lastname: Chaffanet
authors.forename: Patrice
authors.initials: P
authors.lastname: Viens
authors.forename: Daniel
authors.initials: D
authors.lastname: Birnbaum
authors.affiliation: Department of Molecular Oncology, Centre de Recherche en Cancérologie de Marseille, UMR1068 Inserm, Institut Paoli-Calmettes (IPC), Marseille, France. bertuccif@ipc.unicancer.fr.
authors.forename: François
authors.initials: F
authors.lastname: Bertucci
mesh_terms: D001943:Breast Neoplasms / Q000145:classification / Q000235:genetics* / Q000378:metabolism / Q000473:pathology*; D057167:Claudins / Q000235:genetics / Q000378:metabolism*; D018572:Disease-Free Survival; D005260:Female; D020869:Gene Expression Profiling; D015972:Gene Expression Regulation, Neoplastic; D015894:Genome, Human / Q000235:genetics; D006801:Humans; D008875:Middle Aged; D016017:Odds Ratio; D011379:Prognosis; D016016:Proportional Hazards Models; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism
chemical_list: D057167:Claudins; D012333:RNA, Messenger