Circulating DNA in EGFR-mutated lung cancer

Circulating tumor DNA (ctDNA) consists of short double stranded DNA fragments that are released by tumors including non-small cell lung cancer (NSCLC). With the identification of driver mutations in the epidermal growth factor receptor (EGFR) gene and development of targeted tyrosine kinase inhibitors (TKIs), the clinical outcome of NSCLC patients in this subgroup has improved tremendously. The gold standard to assess EGFR mutation is through tissue biopsy, which can be limited by difficulty in accessing the tumor, inability of patients to tolerate invasive procedures, insufficient sample for molecular testing and inability to capture intratumoral heterogeneity. The great need for rapid and accurate identification of activating EGFR mutations in NSCLC patients paves the road for ctDNA technology. Studies have demonstrated ctDNA to be a reliable complement to tumor genotyping. Platforms like digital polymerase chain reaction (PCR) and next-generation sequencing based analyses have made it possible to identify EGFR mutations in plasma with high sensitivity and specificity. This article will provide an overview on ctDNA in the context of EGFR mutated NSCLC, especially its emerging applications in diagnosis, disease surveillance, treatment monitoring and detection of resistance mechanisms.