SOX2 and neoplasm: Cells from another NPC cell line, C666-1 which grew as free-floating spheres, displayed stemness characteristics such as a propensity for tumour formation, contained higher expression levels of pluripotent genes SOX2 and KLF4 as well as metastasis-associated gene CD44 than the normally adherent ones, and had higher tumourigenic potential in vivo8.