DNA methylation biomarkers in biological fluids for early detection of respiratory tract cancer

Cancers of the respiratory tract (lung and head and neck) share common aetiologies, risk factors and molecular characteristics. Epigenetic reprogramming is one of the hallmarks of cancer and DNA methylation is currently the best-studied form. There are a number of characteristics of DNA methylation, which seem advantageous in biomarker development. Early detection is still an unmet clinical care need, which guarantees to significantly reduce the mortality of patients with respiratory cancers. The application of such biomarkers in biological fluids being sampled in everyday clinical practice is a long-term demand. In this review we summarise the current literature on DNA methylation detection in bronchial washings, sputum, saliva, plasma and serum and discuss the potential of their clinical implementation. We also discuss important aspects of biomarker development and validation pointing to the appropriate route for a biomarker to reach clinical standards.