To further confirm that podocalyxin has a causal role in promoting tumorsphere formation in vitro, we overexpressed PODXL in MCF7 cells (MCF7Podxl) (Additional file 3C), a luminal-like human breast cancer cell line that expresses very low levels of endogenous podocalyxin [10,19]. The gene discussed is PODXL; the disease is breast carcinoma.