Plasticity and intratumoural heterogeneity of cell surface antigen expression in breast cancer

Background: The intratumoural heterogeneity, often driven by epithelial-to-mesenchymal transition (EMT), significantly contributes to chemoresistance and disease progression in adenocarcinomas. Methods: We introduced a high-throughput screening platform to identify surface antigens that associate with epithelial–mesenchymal plasticity in well-defined pairs of epithelial cell lines and their mesenchymal counterparts. Using multicolour flow cytometry, we then analysed the expression of 10 most robustly changed antigens and identified a 10-molecule surface signature, in pan-cytokeratin-positive/EpCAM-positive and -negative fractions of dissociated breast tumours. Results: We found that surface CD9, CD29, CD49c, and integrin β5 are lost in breast cancer cells that underwent EMT in vivo . The tetraspanin family member CD9 was concordantly downregulated both in vitro and in vivo and associated with epithelial phenotype and favourable prognosis. Conclusions: We propose that overall landscape of 10-molecule surface signature expression reflects the epithelial–mesenchymal plasticity in breast cancer.