A biomarker is any characteristic that can be measured, providing a diagnostic or prognostic indication of disease presence or severity. Biomarkers are a less-invasive method for analyzing a disease state than a biopsy in which the skin is incised and portions of diseased tissue are removed for pathology analysis. The nature of a biomarker depends on the modality of the biomarker analysis used; biomarkers can range from a stereotypical signature via MRI or CT scan, to tumor-related exosomes isolated from blood, urine, saliva, or cerebrospinal fluid. Biomarkers
enable the monitoring of disease states that would otherwise require more invasive methods to follow. Recently, the term liquid biopsy
has been used to describe the collection of body fluids for the identification of biomarkers contained therein. Liquid biopsies represent a non-invasive alternative to traditional, surgical biopsies.