BMI1 and nasopharyngeal carcinoma: In our study, we observed a high expression of PTK6 in most NPC cell lines include CNE1, CNE2, 6-10B, 5-8F, HONE1 and SUNE1 at both mRNA and protein level, but not in a highly differentiated NPC cell line HNE1, NPEC1 Bmi-1 or NPEC2 Bmi-1 cells.