DAPK1 and head and neck squamous cell carcinoma: Since increased DAPK1 gene methylation has been associated with persistent HPV infection [38] and the promoter region of DAPK1 has also been shown to be hypermethylated in HNSCC [18], we investigated the methylation status of the DAPK1 promoter in a panel of six HNSCC cell lines, an oral dysplastic cell line, and a basaloid squamous cell carcinoma cell line (all cultured in methyl donor containing medium).