title: Topoisomerase 1(TOP1) gene copy number in stage III colorectal cancer patients and its relation to prognosis.
abstract: OBJECTIVE
  A Topoisomerase 1 (Top1) poison is frequently included in the treatment regimens for metastatic colorectal cancer (mCRC). However, no predictive biomarkers for Top1 poisons are available. We here report a study on the TOP1 gene copy number in CRC patients and its association with patient prognosis and tumor cell proliferation.
  
  
  METHODS
  The study included TOP1 and CEN-20 fluorescence in situ hybridization (FISH) analyses on formalin fixed paraffin embedded (FFPE) tissue sections from 154 stage III CRC chemonaïve patients. The frequencies of aberration in the TOP1 gene copy number, the CEN-20 copy number and the TOP1/CEN-20 ratio were analyzed and associated with overall survival (OS), time to recurrence (TTR) and in a subgroup analysis of rectal cancer patients only with time to local recurrence (LR in RC). Moreover, the TOP1 and CEN-20 copy numbers were correlated with the tumor Ki67 proliferation index.
  
  
  RESULTS
  35.7% of the tumors had an increased TOP1 copy number above 4n gene copies per cell and 28.6% and 9.7% had a TOP1/CEN-20 ratio ≥1.5 or ≥2.0, respectively. The TOP1 copy number and the TOP1/CEN-20 ratios were separately added into multivariate analyses as continuous variables, in which also age, gender, primary tumor location and Ki67 status were added as covariates. In contrast to the TOP1/CEN-20 ratio, the TOP1 copy number was significantly associated with OS (HR: 0.62; 95% CI: 0.42-0.90; p = 0.01). Neither the TOP1 copy number nor the ratio was significantly associated with TTR and only the TOP1/CEN-20 ratio was significantly associated with LR in RC (HR: 0.25; 95% CI: 0.08-0.83; p = 0.02). No significant correlation was found between the TOP1 copy number and proliferation, while a weak and inverse correlation between the CEN-20 copy number and proliferation was observed.
  
  
  CONCLUSIONS
  This study showed that increased TOP1 gene copy numbers are frequent findings in cancer cells in stage III CRC tumors but unrelated to the proliferative status of the tumors. The association with prognosis is important to consider when planning and analyzing future studies investigating TOP1 as a potential predictive biomarker for Top1 poisons.
authors.affiliation: Section of Pathobiology, Department of Veterinary Disease Biology, Faculty of Health and Medical Sciences, University of Copenhagen, Dyrlægevej 88, DK-1870 Frederiksberg, Denmark. romer@life.ku.dk
authors.forename: Maria Unni
authors.initials: MU
authors.lastname: Rømer
authors.forename: Sune Boris
authors.initials: SB
authors.lastname: Nygård
authors.forename: Ib Jarle
authors.initials: IJ
authors.lastname: Christensen
authors.forename: Signe Lykke
authors.initials: SL
authors.lastname: Nielsen
authors.forename: Kirsten Vang
authors.initials: KV
authors.lastname: Nielsen
authors.forename: Sven
authors.initials: S
authors.lastname: Müller
authors.forename: David Hersi
authors.initials: DH
authors.lastname: Smith
authors.forename: Ben
authors.initials: B
authors.lastname: Vainer
authors.forename: Hans Jørgen
authors.initials: HJ
authors.lastname: Nielsen
authors.forename: Nils
authors.initials: N
authors.lastname: Brünner
mesh_terms: D015179:Colorectal Neoplasms / Q000235:genetics*; D004264:DNA Topoisomerases, Type I / Q000235:genetics*; D018628:Gene Dosage / Q000235:genetics*; D006801:Humans; D017403:In Situ Hybridization; D011379:Prognosis
chemical_list: D004264:DNA Topoisomerases, Type I