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.