title: Measurements of EGFR expression on circulating tumor cells are reproducible over time in metastatic breast cancer patients.
abstract: OBJECTIVE
  Studies of EGFR expression in breast cancer have shown inconsistent results due in part to a large range of methods used. Anti-EGFR therapy trials have often not used patient selection because of this. We describe the use of the CellSearch system (Veridex LLC, NJ, USA) to enumerate and measure EGFR expression on the surface of circulating tumor cells (CTCs), derived from the peripheral blood of individuals with metastatic breast cancer over time.
  
  
  METHODS
  The CellSearch system was used to quantify CTCs and EGFR measurement was performed on all samples. The specificity of EGFR phenotyping was further examined by spiking with cell lines with increased and low (or absent) levels of EGFR expression using the CellSearch system to enrich and phenotype the CTCs.
  
  
  RESULTS
  Serial samples were obtained from 33 individuals with metastatic breast cancer. CTCs derived from these individuals had consistent levels of EGFR expression at different time points, and none of the patients 'switched' from a positive to negative EGFR phenotype or vice versa. The specificity of EGFR phenotyping by the CellSearch system was verified by staining of EGFR only being present in a high EGFR expressing EGFR cell line (MDA-MB-468), as confirmed by Western blotting.
  
  
  CONCLUSIONS
  Measurement of EGFR on the surface of CTCs, derived from individuals with metastatic breast cancer patients is possible using the CellSearch system and showed consistent positivity over time. The use of this system will now be validated in a prospective study aiming to identify patients for anti-EGFR therapy based on the expression profile of CTCs.
authors.affiliation: Department of Oncology, Imperial College London, Du Cane Road, London W12 ONN, UK.
authors.forename: Rachel E
authors.initials: RE
authors.lastname: Payne
authors.forename: Ernesto
authors.initials: E
authors.lastname: Yagüe
authors.forename: Martin J
authors.initials: MJ
authors.lastname: Slade
authors.forename: Christos
authors.initials: C
authors.lastname: Apostolopoulos
authors.forename: Long R
authors.initials: LR
authors.lastname: Jiao
authors.forename: Becky
authors.initials: B
authors.lastname: Ward
authors.forename: R Charles
authors.initials: RC
authors.lastname: Coombes
authors.forename: Justin
authors.initials: J
authors.lastname: Stebbing
mesh_terms: D014408:Biomarkers, Tumor / Q000097:blood*; D015153:Blotting, Western; D001943:Breast Neoplasms / Q000097:blood* / Q000378:metabolism / Q000473:pathology; D018929:Cell Culture Techniques / Q000295:instrumentation / Q000379:methods; D066246:ErbB Receptors / Q000096:biosynthesis / Q000097:blood*; D005260:Female; D006801:Humans; D009362:Neoplasm Metastasis; D009360:Neoplastic Cells, Circulating / Q000378:metabolism* / Q000473:pathology; D011237:Predictive Value of Tests; D011446:Prospective Studies; D015203:Reproducibility of Results
chemical_list: D014408:Biomarkers, Tumor; C512478:EGFR protein, human; D066246:ErbB Receptors