State of the art and trends of circulating cancer biomarkers.

The role of biomarkers is crucial in oncology for both early diagnosis and the personalization of cancer treatments. Tissue biomarkers have gained a central role as predictors of the response to an increasing number of anticancer agents; conversely, the clinical role of circulating biomarkers (c-TMs) is limited and has remained almost unchanged over the years. The position of guidelines is summarized and discussed with reference to the potential usefulness of c-TMs in those areas of application that cannot be covered by tissue biomarkers. The pipeline of translational research on biomarkers is briefly described; the differences among analytical validation, clinical validation, and clinical utility are discussed, emphasizing that the assessment of clinical utility is the ultimate step toward clinical use. The role of monitoring of appropriateness as a proxy indicator of how the research pipeline has actually worked is discussed, and data and c-TMs overordering rates are reported. The role and limits of guidelines to influence appropriate c-TMs ordering are discussed. The design of primary studies on c-TMs is examined, underlining that they mainly focus on clinical validation rather than on clinical utility. The role of regulatory boards is also briefly presented and discussed.