RASSF1 and head and neck squamous cell carcinoma: With regard to ctDNA methylation in saliva samples, Lim et al. found that the RASSF1α, CDKN2A, TIMP3, and PCQAP/MED15 genes had higher methylation levels in HPV-negative HNSCC patients than in healthy controls, while the same genes had lower methylation levels in HPV-positive HNSCC patients than in healthy controls [73].