EGFR and lung cancer: One of the earliest applications of ctDNA detection is to identify epidermal growth factor receptor (EGFR) mutations for the guidance of EGFR inhibitor therapy in non-small cell lung cancer (NSCLC), which has been approved by the Food and Drug Administration (FDA) [24] and further included in the new College of American Pathologists (CAP)/International Association for the Study of Lung Cancer (IASLC)/Association for Molecular Pathology (AMP) testing guidelines [25].