From a clinical perspective, biomarkers may have a variety of functions, which correspond to different stages (table 1) in disease development, such as in the progression in cancer or cardiovascular disease.1 2 Biomarkers can assist in the care of patients who are asymptomatic (screening biomarkers), those who are suspected to have the disease (diagnostic biomarkers) and those with overt disease (prognostic biomarkers) for whom therapy may or may not have been initiated. Biomarkers can also be used for treatment response (predictive biomarkers) or surveillance after therapy (monitoring biomarkers). Fundamental for the use of biomarkers in all situations is biomarker accuracy—the ability to correctly classify one condition and/or outcome from another (eg, healthy versus diseased).

For the clinician, diagnostic testing plays a fundamental role in clinical practice. For instance, daily surgical decision making is based on the correct classification by pathology, radiology and/or clinical chemistry reports involving tissue and/or image evaluation and interpretation of disease conditions—in many decisions the interpretation is based on results in the “grey-area” although requiring “black-and-white” answers for choice of treatment (fig 1). Further, predictive modelling to estimate expected outcomes such as mortality or adverse events based on patient risk characteristics is common in any type of clinical research. Receiver-operating characteristic (ROC) …