title: Challenges in the enumeration and phenotyping of CTC.
abstract: OBJECTIVE
  Presence of circulating tumor cells (CTC) in metastatic carcinoma is associated with poor survival. Phenotyping and genotyping of CTC may permit "real-time" treatment decisions, provided CTCs are available for examination. Here, we investigate what is needed to detect CTC in all patients.
  
  
  METHODS
  CTCs enumerated in 7.5 mL of blood together with survival from 836 patients with metastatic breast, colorectal, and prostate cancer were used to predict the CTC concentration in the 42% of these patients in whom no CTCs were found and to establish the relation of concentration of CTCs with survival. Influence of different CTC definitions were investigated by automated cell recognition and a flow cytometric assay without an enrichment or permeabilization step.
  
  
  RESULTS
  A log-logistic regression of the log of CTC yielded a good fit to the CTC frequency distribution. Extrapolation of the blood volume to 5 L predicted that 99% of patients had at least one CTC before therapy initiation. Survival of patients with EpCAM+, cytokeratin+, CD45- nucleated CTCs is reduced by 6.6 months for each 10-fold CTC increase. Using flow cytometry, the potential three-fold recovery improvement is not sufficient to detect CTC in all patients in 7.5 mL of blood.
  
  
  CONCLUSIONS
  EpCAM+, cytokeratin+, CD45- nucleated CTCs are present in all patients with metastatic breast, prostate, and colorectal cancer and their frequency is proportional to survival. To serve as a liquid biopsy for the majority of patients, a substantial improvement of CTC yield is needed, which can only be achieved by a dramatic increase in sample volume.
authors.affiliation: Department of Medical Cell BioPhysics, MIRA institute, University of Twente, Enschede, The Netherlands.
authors.forename: Frank A W
authors.initials: FA
authors.lastname: Coumans
authors.forename: Sjoerd T
authors.initials: ST
authors.lastname: Ligthart
authors.forename: Jonathan W
authors.initials: JW
authors.lastname: Uhr
authors.forename: Leon W M M
authors.initials: LW
authors.lastname: Terstappen
mesh_terms: D000328:Adult; D000368:Aged; D000951:Antigens, Neoplasm / Q000097:blood; D014408:Biomarkers, Tumor / Q000097:blood*; D015815:Cell Adhesion Molecules / Q000097:blood; D002452:Cell Count; D045744:Cell Line, Tumor; D000071858:Epithelial Cell Adhesion Molecule; D005260:Female; D005434:Flow Cytometry; D006801:Humans; D007633:Keratins / Q000097:blood; D017493:Leukocyte Common Antigens / Q000097:blood; D008297:Male; D008875:Middle Aged; D009362:Neoplasm Metastasis / Q000175:diagnosis; D009367:Neoplasm Staging; D009369:Neoplasms / Q000097:blood / Q000175:diagnosis / Q000473:pathology; D009360:Neoplastic Cells, Circulating / Q000378:metabolism*; D011379:Prognosis
chemical_list: D000951:Antigens, Neoplasm; D014408:Biomarkers, Tumor; D015815:Cell Adhesion Molecules; C499379:EPCAM protein, human; D000071858:Epithelial Cell Adhesion Molecule; D007633:Keratins; D017493:Leukocyte Common Antigens; C516769:PTPRC protein, human