SFRP1 and head and neck squamous cell carcinoma: The methylation pattern of CCNA1, DAPK, MGMT, SFRP1 and TIMP3 as well as a panel containing all these 5 genes was analyzed for potential associations with clinical and pathological characteristics of HNSCC patients, including age, gender, tobacco consumption, alcohol consumption, primary tumor site, T stage, N stage, lymph vascular invasion, perineural invasion, surgical margins status, lymph node involvement and second primary tumor development.