RASSF1 and head and neck cancer: Cohort of salivary cell pellet from 174 subjects: 31 healthy volunteers and 143 head and neck cancers (HNSCCs)The promoter methylation levels of p16INK4a, RASSF1A, and DAPK1 in salivary DNA from 143 head-and-neck-cancer patients and 31 healthy non-smoker controlsA sensitive methylation-specific polymerase chain reaction (MSP) assay; nested MSP