CD24 and neoplasm: Flow cytometry for epithelial (CD24) and mesenchymal (PDGFR-β or CD49e) proteins confirmed the epithelial nature of orthotopic primary H2B-eGFP-labeled HER2/neu tumors, and further revealed rare populations of mesenchymal CD24–PDGRF-(beta)+ and CD24–CD49e+ primary tumor cells that were dramatically enriched in MRLs following HER2/neu downregulation (Additional file 7: Fig. S5d-g).