Furthermore, in patients with overt cancer, the abundance of cpDNA that likely originates from the cancerous cells offers the possibility to use this source material as a non-invasive monitoring system for applying companion diagnostics to determine an appropriate lung cancer treatment, as was recently shown for the detection of epidermal growth factor receptor (EGFR) mutations for EGFR-tyrosine kinase inhibitors (24). The gene discussed is EGFR; the disease is cancer.