Circulating tumour cell enumeration using the CellSearch system (Veridex LLC, Raritan, NJ, USA) was carried out according to the manufacturer's protocol and training. Blood samples were processed on the CellTracks Autoprep within 72 h. Epithelial cells were immunomagnetically enriched using ferrofluids coated with EpCAM-specific antibodies, then permeabilised and fluorescently labelled with phycoerythrin-conjugated antibodies directed against cytokeratin 8, 18 and 19, an allophycocyanin-conjugated antibody to CD45 and the nuclear dye DAPI. After transfer to a cartridge in a MagNest, labelled cells were analysed on the CellTracks Analyser II, a four-colour semi-automated fluorescent microscope that captures images of the entire surface of the cartridge for the four fluorescent dyes. From the captured images, a gallery of objects was presented to a trained operator (technician) who interprets each object. According to manufacturer guidelines, an object defined as a CTC should meet all of the following criteria: (i) an intact cell with a round to oval morphology and at least 4 μm in size; (ii) positive for DAPI with a nucleus inside the cytoplasm (of at least >50%) and a nucleus area smaller than the cytoplasm; (iii) positive for cytokeratins (bright or moderate) and negative for CD45 and the blank channel. Each sample was analysed independently by two trained technicians (NV and NJ).
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