title: The functional loss of the retinoblastoma tumour suppressor is a common event in basal-like and luminal B breast carcinomas.
abstract: BACKGROUND
  Breast cancers can be classified using whole genome expression into distinct subtypes that show differences in prognosis. One of these groups, the basal-like subtype, is poorly differentiated, highly metastatic, genomically unstable, and contains specific genetic alterations such as the loss of tumour protein 53 (TP53). The loss of the retinoblastoma tumour suppressor encoded by the RB1 locus is a well-characterised occurrence in many tumour types; however, its role in breast cancer is less clear with many reports demonstrating a loss of heterozygosity that does not correlate with a loss of RB1 protein expression.
  
  
  METHODS
  We used gene expression analysis for tumour subtyping and polymorphic markers located at the RB1 locus to assess the frequency of loss of heterozygosity in 88 primary human breast carcinomas and their normal tissue genomic DNA samples.
  
  
  RESULTS
  RB1 loss of heterozygosity was observed at an overall frequency of 39%, with a high frequency in basal-like (72%) and luminal B (62%) tumours. These tumours also concurrently showed low expression of RB1 mRNA. p16INK4a was highly expressed in basal-like tumours, presumably due to a previously reported feedback loop caused by RB1 loss. An RB1 loss of heterozygosity signature was developed and shown to be highly prognostic, and was potentially a predictive marker of response to neoadjuvant chemotherapy.
  
  
  CONCLUSIONS
  These results suggest that the functional loss of RB1 is common in basal-like tumours, which may play a key role in dictating their aggressive biology and unique therapeutic responses.
authors.affiliation: Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill, 27599, USA.
authors.forename: Jason I
authors.initials: JI
authors.lastname: Herschkowitz
authors.forename: Xiaping
authors.initials: X
authors.lastname: He
authors.forename: Cheng
authors.initials: C
authors.lastname: Fan
authors.forename: Charles M
authors.initials: CM
authors.lastname: Perou
mesh_terms: D001943:Breast Neoplasms / Q000145:classification / Q000188:drug therapy / Q000235:genetics* / Q000473:pathology; D002277:Carcinoma / Q000145:classification / Q000188:drug therapy / Q000235:genetics* / Q000473:pathology; D002455:Cell Division; D019938:Cyclin D1 / Q000096:biosynthesis; D019941:Cyclin-Dependent Kinase Inhibitor p16 / Q000096:biosynthesis; D019008:Drug Resistance, Neoplasm / Q000235:genetics; D005260:Female; D020869:Gene Expression Profiling; D016161:Genes, Retinoblastoma; D019940:Genes, bcl-1; D019942:Genes, p16; D006801:Humans; D019656:Loss of Heterozygosity; D020360:Neoadjuvant Therapy; D009363:Neoplasm Proteins / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D020411:Oligonucleotide Array Sequence Analysis; D012333:RNA, Messenger / Q000096:biosynthesis; D012334:RNA, Neoplasm / Q000096:biosynthesis; D016160:Retinoblastoma Protein / Q000096:biosynthesis / Q000502:physiology*
chemical_list: C530104:CCND1 protein, human; D019941:Cyclin-Dependent Kinase Inhibitor p16; D009363:Neoplasm Proteins; D012333:RNA, Messenger; D012334:RNA, Neoplasm; D016160:Retinoblastoma Protein; D019938:Cyclin D1
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