As CD24, CD44 and EpCAM were frequently used to isolate tumourigenic cells18,21,25,34,35, their expression levels were assessed in NPC cell lines (HK1 and C666-1 cell lines) and early-passage PDXs (xeno-284 and xeno-B110) by flow cytometry (Fig. 1). The gene discussed is CD44; the disease is nasopharyngeal carcinoma.