CYB5R2 and nasopharyngeal carcinoma: Having established that CYB5R2 was downregulated in NPC cell lines and primary biopsies, we further investigated the promoter methylation status of CYB5R2. MSP results showed that the CYB5R2 promoter was hypermethylated in the six NPC cell lines (CNE1, CNE2, TW03, HONE1, HNE1 and C666-1; see Fig. 2a) and in 84 % (42/50) of NPC primary tumors but in none of the 12 NNE samples (Fig. 2b).