title: Gene expression profiles in circulating tumor cells to predict prognosis in metastatic breast cancer patients.
abstract: BACKGROUND
  A circulating tumor cell (CTC) count is an established prognostic factor in metastatic breast cancer (MBC). Besides enumeration, CTC characterization promises to improve outcome prediction and treatment guidance. Having shown the feasibility of quantifying clinically relevant mRNA transcripts in CTCs, we determined the prognostic value of CTC gene expression in MBC.
  
  
  METHODS
  CTCs were isolated and enumerated from blood of 197 MBC patients who were about to start first-line systemic therapy. Of these, 180 were assessable for quantification of mRNA expression by RT-qPCR in relation to time-to-treatment failure (TTF). A prognostic CTC gene profile was generated by leave-one-out cross validation in a 103 patient discovery set and validated in 77 patients. Additionally, all 180 patients were randomly divided into two equal sets to discover and validate a second prognostic profile.
  
  
  RESULTS
  CTC count predicted for TTF at baseline {≥5 versus <5 CTCs/7.5 ml blood, hazard ratio (HR) 2.92 [95% confidence interval (CI) 1.71-4.95] P < 0.0001}. A 16-gene CTC profile was generated in the first discovery set, which identified patients with death or TTF <9 months versus those with a better outcome. In multivariate analysis, the 16-gene profile was the only factor associated with TTF [HR 3.15 (95% CI 1.35-7.33) P 0.008]. Validation of this profile in the independent patient set pointed into the same direction, but was not statistically significant. A newly generated 8-gene profile showed similarly favorable test characteristics as the 16-gene profile, but did not significantly pass validation either.
  
  
  CONCLUSIONS
  A 16-gene CTC profile was identified, which provided prognostic value on top of CTC count in MBC patients. However, validation of this profile in an independent cohort, nor of a second profile, reached statistical significance, underscoring the need to further fine-tune the still promising approach of CTC characterization.
authors.affiliation: Department of Medical Oncology.
authors.forename: B
authors.initials: B
authors.lastname: Mostert
authors.affiliation: Department of Medical Oncology Department of Medical Oncology and Cancer Genomics Netherlands, Erasmus MC Cancer Institute, Erasmus University Medical Center, Rotterdam, The Netherlands.
authors.forename: A M
authors.initials: AM
authors.lastname: Sieuwerts
authors.affiliation: Department of Medical Oncology.
authors.forename: J
authors.initials: J
authors.lastname: Kraan
authors.affiliation: Department of Medical Oncology.
authors.forename: J
authors.initials: J
authors.lastname: Bolt-de Vries
authors.affiliation: Department of Medical Oncology.
authors.forename: P
authors.initials: P
authors.lastname: van der Spoel
authors.affiliation: Department of Medical Oncology.
authors.forename: A
authors.initials: A
authors.lastname: van Galen
authors.affiliation: Translational Cancer Research Unit, Center for Oncological Research, GZA Hospitals Sint-Augustinus and University of Antwerp, Antwerp, Belgium.
authors.forename: D J
authors.initials: DJ
authors.lastname: Peeters
authors.affiliation: Translational Cancer Research Unit, Center for Oncological Research, GZA Hospitals Sint-Augustinus and University of Antwerp, Antwerp, Belgium.
authors.forename: L Y
authors.initials: LY
authors.lastname: Dirix
authors.affiliation: Department of Medical Oncology.
authors.forename: C M
authors.initials: CM
authors.lastname: Seynaeve
authors.affiliation: Department of Medical Oncology.
authors.forename: A
authors.initials: A
authors.lastname: Jager
authors.affiliation: Ikazia Hospital, Rotterdam.
authors.forename: F E
authors.initials: FE
authors.lastname: de Jongh
authors.affiliation: Sint Franciscus Gasthuis, Rotterdam.
authors.forename: P
authors.initials: P
authors.lastname: Hamberg
authors.affiliation: Maasstad Hospital, Rotterdam.
authors.forename: J M L
authors.initials: JM
authors.lastname: Stouthard
authors.affiliation: Department of Internal Medicine, IJsselland Hospital, Capelle aan den IJssel, The Netherlands.
authors.forename: D F S
authors.initials: DF
authors.lastname: Kehrer
authors.affiliation: Department of Medical Oncology.
authors.forename: M P
authors.initials: MP
authors.lastname: Look
authors.affiliation: Department of Medical Oncology.
authors.forename: M
authors.initials: M
authors.lastname: Smid
authors.affiliation: Department of Medical Oncology.
authors.forename: J W
authors.initials: JW
authors.lastname: Gratama
authors.affiliation: Department of Medical Oncology.
authors.forename: J A
authors.initials: JA
authors.lastname: Foekens
authors.affiliation: Department of Medical Oncology Department of Medical Oncology and Cancer Genomics Netherlands, Erasmus MC Cancer Institute, Erasmus University Medical Center, Rotterdam, The Netherlands.
authors.forename: J W M
authors.initials: JW
authors.lastname: Martens
authors.affiliation: Department of Medical Oncology Department of Medical Oncology and Cancer Genomics Netherlands, Erasmus MC Cancer Institute, Erasmus University Medical Center, Rotterdam, The Netherlands s.sleijfer@erasmusmc.nl.
authors.forename: S
authors.initials: S
authors.lastname: Sleijfer
mesh_terms: D000328:Adult; D001530:Belgium / Q000453:epidemiology; D014408:Biomarkers, Tumor / Q000235:genetics*; D001943:Breast Neoplasms / Q000175:diagnosis* / Q000453:epidemiology / Q000235:genetics*; D015331:Cohort Studies; D005260:Female; D020869:Gene Expression Profiling / Q000379:methods*; D006801:Humans; D008875:Middle Aged; D009360:Neoplastic Cells, Circulating; D009426:Netherlands / Q000453:epidemiology; D011379:Prognosis; D011446:Prospective Studies
chemical_list: D014408:Biomarkers, Tumor
keywords: RT-qPCR; breast cancer; circulating tumor cells; gene expression; prediction; prognosis