Some notable clinical applications of circulating biomarkers include the quantitative real-time polymerase chain reaction (qPCR)-based test recently approved by the US Food and Drug Administration (FDA) for EGFR mutations in circulating cell-free DNA from patients with NSCLC, enabling identification of patients likely to respond to EGFR inhibitors [85], and the FDA-approved CELLSEARCH® test for enumeration of CTCs of epithelial origin to aid in the monitoring of patients with metastatic breast, colorectal or prostate cancers [86]. Here, EGFR is linked to prostate carcinoma.