title: Characterisation of retinoblastomas without RB1 mutations: genomic, gene expression, and clinical studies.
abstract: BACKGROUND
  Retinoblastoma is the childhood retinal cancer that defined tumour-suppressor genes. Previous work shows that mutation of both alleles of the RB1 retinoblastoma suppressor gene initiates disease. We aimed to characterise non-familial retinoblastoma tumours with no detectable RB1 mutations.
  
  
  METHODS
  Of 1068 unilateral non-familial retinoblastoma tumours, we compared those with no evidence of RB1 mutations (RB1(+/+)) with tumours carrying a mutation in both alleles (RB1(-/-)). We analysed genomic copy number, RB1 gene expression and protein function, retinal gene expression, histological features, and clinical data.
  
  
  RESULTS
  No RB1 mutations (RB1(+/+)) were reported in 29 (2·7%) of 1068 unilateral retinoblastoma tumours. 15 of the 29 RB1(+/+) tumours had high-level MYCN oncogene amplification (28-121 copies; RB1(+/+)MYCN(A)), whereas none of 93 RB1(-/-) primary tumours tested showed MYCN amplification (p<0·0001). RB1(+/+)MYCN(A) tumours expressed functional RB1 protein, had fewer overall genomic copy-number changes in genes characteristic of retinoblastoma than did RB1(-/-) tumours, and showed distinct aggressive histological features. MYCN amplification was the sole copy-number change in one RB1(+/+)MYCN(A) retinoblastoma. One additional MYCN(A) tumour was discovered after the initial frequencies were determined, and this is included in further analyses. Median age at diagnosis of the 17 children with RB1(+/+)MYCN(A) tumours was 4·5 months (IQR 3·5-10), compared with 24 months (15-37) for 79 children with non-familial unilateral RB1(-/-) retinoblastoma.
  
  
  CONCLUSIONS
  Amplification of the MYCN oncogene might initiate retinoblastoma in the presence of non-mutated RB1 genes. These unilateral RB1(+/+)MYCN(A) retinoblastomas are characterised by distinct histological features, only a few of the genomic copy-number changes that are characteristic of retinoblastoma, and very early age of diagnosis.
  
  
  BACKGROUND
  National Cancer Institute-National Institutes of Health, Canadian Institutes of Health Research, German Research Foundation, Canadian Retinoblastoma Society, Hyland Foundation, Toronto Netralaya and Doctors Lions Clubs, Ontario Ministry of Health and Long Term Care, UK-Essen, and Foundations Avanti-STR and KiKa.
authors.affiliation: Impact Genetics and the Toronto Western Hospital Research Institute, University Health Network, Toronto, ON, Canada.
authors.forename: Diane E
authors.initials: DE
authors.lastname: Rushlow
authors.forename: Berber M
authors.initials: BM
authors.lastname: Mol
authors.forename: Jennifer Y
authors.initials: JY
authors.lastname: Kennett
authors.forename: Stephanie
authors.initials: S
authors.lastname: Yee
authors.forename: Sanja
authors.initials: S
authors.lastname: Pajovic
authors.forename: Brigitte L
authors.initials: BL
authors.lastname: Thériault
authors.forename: Nadia L
authors.initials: NL
authors.lastname: Prigoda-Lee
authors.forename: Clarellen
authors.initials: C
authors.lastname: Spencer
authors.forename: Helen
authors.initials: H
authors.lastname: Dimaras
authors.forename: Timothy W
authors.initials: TW
authors.lastname: Corson
authors.forename: Renée
authors.initials: R
authors.lastname: Pang
authors.forename: Christine
authors.initials: C
authors.lastname: Massey
authors.forename: Roseline
authors.initials: R
authors.lastname: Godbout
authors.forename: Zhe
authors.initials: Z
authors.lastname: Jiang
authors.forename: Eldad
authors.initials: E
authors.lastname: Zacksenhaus
authors.forename: Katherine
authors.initials: K
authors.lastname: Paton
authors.forename: Annette C
authors.initials: AC
authors.lastname: Moll
authors.forename: Claude
authors.initials: C
authors.lastname: Houdayer
authors.forename: Anthony
authors.initials: A
authors.lastname: Raizis
authors.forename: William
authors.initials: W
authors.lastname: Halliday
authors.forename: Wan L
authors.initials: WL
authors.lastname: Lam
authors.forename: Paul C
authors.initials: PC
authors.lastname: Boutros
authors.forename: Dietmar
authors.initials: D
authors.lastname: Lohmann
authors.forename: Josephine C
authors.initials: JC
authors.lastname: Dorsman
authors.forename: Brenda L
authors.initials: BL
authors.lastname: Gallie
mesh_terms: D000483:Alleles; D045744:Cell Line, Tumor; D002648:Child; D002675:Child, Preschool; D005260:Female; D005784:Gene Amplification; D018628:Gene Dosage; D015972:Gene Expression Regulation, Neoplastic; D015894:Genome, Human; D006801:Humans; D007223:Infant; D009154:Mutation; D000071447:N-Myc Proto-Oncogene Protein; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D015513:Oncogene Proteins / Q000235:genetics / Q000378:metabolism; D020641:Polymorphism, Single Nucleotide; D012175:Retinoblastoma / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D016160:Retinoblastoma Protein / Q000235:genetics / Q000378:metabolism
chemical_list: C459801:MYCN protein, human; D000071447:N-Myc Proto-Oncogene Protein; D009687:Nuclear Proteins; D015513:Oncogene Proteins; D016160:Retinoblastoma Protein