KLF4 and undifferentiated carcinoma: Due to more promising tumourigenicity data, stable TIC frequency during serial transplantation and inverse association with KLF4 mRNA level observed in EpCAMbr xeno-B110 cells, co-staining of EpCAM and KLF4 proteins were performed in a separate set of 10 archival specimens (3 from non-keratinising undifferentiated carcinoma, 6 from non-keratinising differentiated carcinoma and 1 from keratinising squamous cell carcinoma).