title: Intratumoral heterogeneity in a minority of ovarian low-grade serous carcinomas.
abstract: BACKGROUND
  Ovarian low-grade serous carcinoma (LGSC) has fewer mutations than ovarian high-grade serous carcinoma (HGSC) and a less aggressive clinical course. However, an overwhelming majority of LGSC patients do not respond to conventional chemotherapy resulting in a poor long-term prognosis comparable to women diagnosed with HGSC. KRAS and BRAF mutations are common in LGSC, leading to clinical trials targeting the MAPK pathway. We assessed the stability of targetable somatic mutations over space and/or time in LGSC, with a view to inform stratified treatment strategies and clinical trial design.
  
  
  METHODS
  Eleven LGSC cases with primary and recurrent paired samples were identified (stage IIB-IV). Tumor DNA was isolated from 1-4 formalin-fixed paraffin-embedded tumor blocks from both the primary and recurrence (n = 37 tumor and n = 7 normal samples). Mutational analysis was performed using the Ion Torrent AmpliSeqTM Cancer Panel, with targeted validation using Fluidigm-MiSeq, Sanger sequencing and/or Raindance Raindrop digital PCR.
  
  
  RESULTS
  KRAS (3/11), BRAF (2/11) and/or NRAS (1/11) mutations were identified in five unique cases. A novel, non-synonymous mutation in SMAD4 was observed in one case. No somatic mutations were detected in the remaining six cases. In two cases with a single matched primary and recurrent sample, two KRAS hotspot mutations (G12V, G12R) were both stable over time. In three cases with multiple samplings from both the primary and recurrent surgery some mutations (NRAS Q61R, BRAF V600E, SMAD4 R361G) were stable across all samples, while others (KRAS G12V, BRAF G469V) were unstable.
  
  
  CONCLUSIONS
  Overall, the majority of cases with detectable somatic mutations showed mutational stability over space and time while one of five cases showed both temporal and spatial mutational instability in presumed drivers of disease. Investigation of additional cases is required to confirm whether mutational heterogeneity in a minority of LGSC is a general phenomenon that should be factored into the design of clinical trials and stratified treatment for this patient population.
authors.forename: Alicia A
authors.initials: AA
authors.lastname: Tone
authors.forename: Melissa K
authors.initials: MK
authors.lastname: McConechy
authors.forename: Winnie
authors.initials: W
authors.lastname: Yang
authors.forename: Jiarui
authors.initials: J
authors.lastname: Ding
authors.forename: Stephen
authors.initials: S
authors.lastname: Yip
authors.forename: Esther
authors.initials: E
authors.lastname: Kong
authors.forename: Kwong-Kwok
authors.initials: KK
authors.lastname: Wong
authors.forename: David M
authors.initials: DM
authors.lastname: Gershenson
authors.forename: Helen
authors.initials: H
authors.lastname: Mackay
authors.forename: Sohrab
authors.initials: S
authors.lastname: Shah
authors.forename: Blake
authors.initials: B
authors.lastname: Gilks
authors.forename: Anna V
authors.initials: AV
authors.lastname: Tinker
authors.forename: Blaise
authors.initials: B
authors.lastname: Clarke
authors.forename: Jessica N
authors.initials: JN
authors.lastname: McAlpine
authors.affiliation: Department of Pathology and Laboratory Medicine, University of British Columbia, Vancouver, BC, Canada. dhuntsma@bccancer.bc.ca.
authors.forename: David
authors.initials: D
authors.lastname: Huntsman
mesh_terms: D000328:Adult; D018284:Cystadenocarcinoma, Serous / Q000235:genetics* / Q000473:pathology*; D004252:DNA Mutational Analysis; D005260:Female; D020558:GTP Phosphohydrolases / Q000235:genetics; D018740:Genetic Heterogeneity; D006801:Humans; D008565:Membrane Proteins / Q000235:genetics; D008875:Middle Aged; D009154:Mutation; D010051:Ovarian Neoplasms / Q000235:genetics* / Q000473:pathology; D011518:Proto-Oncogene Proteins / Q000235:genetics; D048493:Proto-Oncogene Proteins B-raf / Q000235:genetics; D016283:Proto-Oncogene Proteins p21(ras); D018631:ras Proteins / Q000235:genetics
chemical_list: C117307:KRAS protein, human; D008565:Membrane Proteins; D011518:Proto-Oncogene Proteins; C482119:BRAF protein, human; D048493:Proto-Oncogene Proteins B-raf; D020558:GTP Phosphohydrolases; C579846:NRAS protein, human; D016283:Proto-Oncogene Proteins p21(ras); D018631:ras Proteins