Liquid biopsies based on cell-free DNA as a potential biomarker in head and neck cancer.

In the era of 'precision medicine', liquid biopsies based on cell-free DNA (cfDNA) have emerged as a promising tool in the oncology field. cfDNA from cancer patients is a mixture of tumoral (ctDNA) and non-tumoral DNA originated from healthy, cancer and tumor microenvironmental cells. Apoptosis, necrosis, and active secretion from extracellular vesicles represent the main mechanisms of cfDNA release into the physiological body fluids. Focused on HNC, two main types of cfDNA can be identified: the circulating cfDNA (ccfDNA) and the salivary cfDNA (scfDNA). Numerous studies have reported on the potential of cfDNA analysis as potential diagnostic, prognostic, and monitoring biomarker for HNC. Thus, ctDNA has emerged as an attractive strategy to detect cancer specific genetic and epigenetic alterations including DNA somatic mutations and DNA methylation patterns. This review aims to provide an overview of the up-to-date studies evaluating the value of the analysis of total cfDNA, cfDNA fragment length, and ctDNA analysis at DNA mutation and methylation level in HNC patients.

Methods for the Detection of Circulating Biomarkers in Cancer Patients.

Liquid biopsy has emerged as one of the main pillars for personalized oncology. The term englobes body-fluid samples which contain tumor-derived material such as circulating tumor DNA (ctDNA), circulating tumor cells (CTCs), and circulating extracellular vesicles (cEVs). Potential clinical application of liquid biopsy analyses includes cancer screening, detection of minimal residual disease and recurrence, therapy selection, and evaluation of acquired resistance. Despite the great developments of technology focused on circulating biomarkers characterization only cfDNA testing is nowadays implemented for the therapy selection in some advanced tumors. This can be partially explained by the fact that there is still a lack of global standardization of procedures both in the pre-analytical and analytical steps. In the present chapter, we summarize the different strategies for addressing the study of liquid biopsy taking into account their pros and cons to be applied in a clinical context and we also discuss the main technical and clinical challenges in the field of circulating biomarkers and personalized oncology.

Saliva Gene Promoter Hypermethylation as a Biomarker in Oral Cancer.

Oral carcinogenesis is a multistep process characterized by a summation of multiple genetic and epigenetic alterations in key regulatory genes. The silencing of genes by aberrant promoter hypermethylation is thought to be an important epigenetic event in cancer development and progression which has great potential as a biomarker for early diagnosis, tumor molecular subtyping, prognosis, monitoring, and therapy. Aberrant DNA methylation has been detected in different liquid biopsies, which may represent a potential alternative to solid biopsies. The detection of methylated genes in saliva may have clinical application for noninvasive oral cancer screening and early diagnosis. Here, we review the current evidence on gene promoter hypermethylation in saliva.