Measurements of EGFR expression on circulating tumor cells are reproducible over time in metastatic breast cancer patients

Aims: 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 (TM) 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. Materials & 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.