Circulating tumour DNA in EGFR-mutant non-small-cell lung cancer

The advent of targeted therapy in non-small-cell lung cancer (NSCLC) has made the routine molecular diagnosis of EGFR mutations crucial for optimal patient management. Obtaining tumour tissue for biomarker testing, especially in the setting of re-biopsy, can present many challenges. A potential alternative source of tumour DNA is circulating cell-free tumour-derived DNA (CTDNA). Although CTDNA is present in low quantities in plasma, the convenience of sample acquisition and the increasing reliability of detection methods make this approach a promising one. The various performance characteristics of both digital and nondigital platforms are still variable, and a standardized approach is needed that will make those platforms reliable clinical tools for the detection of EGFR sensitizing mutations and resistance mutations, including the T790M resistance mutation. Information derived from CTDNA can be used to assess tumour burden, to identify genomic-based resistance mechanisms, and to track dynamic changes during therapy.