RASSF1 and nasopharyngeal carcinoma: The frequencies of promoter hypermethylation of RASSF1A and DAPK were 79.6% (39 of 49) and 67.3% (33 of 49) in NPC biopsy samples, while methylated in 57.2% (29 of 49) and 55.1% (27 of 49) respectively in the corresponding swabs.