By qPCR assays, Schröck et al. [36] initially investigated quantitative methylation levels in matched plasma and tumor tissue samples from 55 HNSCC patients and observed a significant correlation between SHOX2 methylation in pretherapeutic plasma and methylation levels in tumor tissue, whereas a trend toward higher plasma SEPT9 methylation was detected in cases SEPT9 hypermethylated tumors. This evidence concerns the gene SHOX2 and head and neck squamous cell carcinoma.