Table 1.

ctDNA biomarkers for HNSCC.

Marker	Type of Marker	Findings	Sample Size	Reference
E7 (HPV16 and HPV18), TP53, PIK3CA, CDKN2A, FBXW7, HRAS, and NRAS	Diagnostic	The sensitivity of detection of ctDNA increased when both saliva and plasma assays were combined (96% of the samples). Moreover, oral cavity tumor ctDNA was preferentially enriched in saliva as opposed to ctDNA from other sites.	93	(28)
CDKN1A and DDB2	Post-treatment monitoring	Salivary CDKN1A and DDB2 were significantly upregulated post-treatment in HNSCC patients and the rate of upregulation was correlated with the received treatment dose.	8	(39)
HPV DNA	Prognostic	Salivary HPV DNA levels in patients with LR HPV+ OPSCC were correlated to total tumor burden. A rise of salivary HPV DNA was correlated with recurrence and a fall in HPV DNA levels was observed during treatment. Higher levels of plasma HPV cfDNA were associated with poor prognosis.	21	(40)