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 beta 5 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.