Circulating tumor cells (CTCs) can be enumerated using CellSearch, but not all breast cancer subtypes, specifically those with epithelial-mesenchymal transition (EMT) characteristics, sufficiently express the enrichment (EpCAM) and selection (CK8/18/19) markers used in this method. While CD146 can detect EpCAM-negative CTCs, we here evaluated the value of various cytokeratins and CD49f to detect CK8/18/19-negative CTCs. The tested cytokeratins provided no substantial benefit, but adding CD49f to CK8/18/19 as a selection marker resulted in improved recovery of normal-like cell lines. Combined staining of CK8/18/19 and CD49f after CD146/EpCAM enrichment is likely to further improve CTC detection in breast cancer.
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