Feasibility of methylated ctDNA detection in plasma samples of oropharyngeal squamous cell carcinoma patients.

Background: Oropharyngeal squamous cell carcinomas (OpSCCs) are commonly associated with high rates of treatment failure.

Objectives: To evaluate methylation-based markers in plasma from OpSCC patients as emerging tools for accurate/noninvasive follow-up.

Methods: Pretreatment formalin-fixed paraffin-embedded (FFPE) biopsies (n = 52) and paired plasma (n = 15) were tested for the methylation of CCNA1, DAPK, CDH8, and TIMP3 by droplet digital PCR (ddPCR).

Results: Seventy-one percent (37/52) of the biopsies showed methylation of at least one of the evaluated genes and tumor CCNA1 methylation was associated with recurrence-free survival. Methylated circulating tumor DNA (meth-ctDNA) was detected in 11/15 (73.3%) plasma samples; conversely, plasma samples from healthy controls were all negative for DNA methylation (area under the curve = 0.867; 95% confidence interval = 0.720-1.000). Additionally, preliminary results on the detection of meth-ctDNA in plasma collected during follow-up closely matched patient outcome.

Conclusions: The results suggest the feasibility of detecting meth-ctDNA in plasma using ddPCR and a possible application on routine setting after further validation.