Development of automated quantitative multiparameter immunocytochemical profiling of circulating tumor cells (CTCs) in breast cancer (BC).

Abstract

e21124 Background: The currently accepted definition of a CTC is a nucleated cell that is positive by qualitative fluorescence for EpCAM, expresses cytokeratin, and is negative for the pan-hematopoietic marker CD45. Such approach has limitations such as operator bias, difficulty distinguishing true signal from autofluoresence or filter bleed-through, and most importantly, it cannot differentiate expression levels that are low, intermediate or high. This is a problem because CTCs are in fact heterogeneous with respect to phenotypic expression of various markers. Methods: Peripheral blood samples were subjected to our previously described, negative depletion technology. Cytospins of enriched samples were stained with 3 to 5 antibodies conjugated to various Alexa Fluor dyes plus a nuclear dye and then analyzed with both confocal microscopy and a traditional epifluorescence microscope equipped with a Nuance (CRi) multispectral imaging camera and associated software. This imaging system allows not only fluorescent signals to be quantified between specific excitation and emission filters, but also the spectral structure between these boundaries through the use of a liquid crystal that takes images in as little as 10nm increments. Such imaging allows spectra from specific dyes to identify from the contributions of other dyes, filter leakage, and auto fluorescence. Results: Using this technology, and appropriate controls, we are developing continuous variable quantification of the expression of: cytokeratins, vimentin, CD45, Her2, CD44, EpCAM and EGFR in negatively enriched, peripheral blood samples from metastatic breast cancer patients. To date, over 10 metastatic patient samples have been quantified and the study is ongoing. Initial quantification indicates that significant variability in expression levels exists in multiple markers including Her2 neu. Conclusions: Using multispectral technology, we have shown that CTCs are heterogeneous, with different CTCs having varying expression levels of EpCAM, HER2 neu, vimentin and EGFR. Further multiparameter quantitative characterization with up to 6 color analysis on the same cell is in progress.