ctDNA Guided Treatment of Early Resistance to Targeted Treatment

Next Generation Sequence (NGS) technology rapidly evolves and it is now feasible to use circulating tumor DNA (ctDNA) as a BioSource for comprehensive analysis of the molecular make up of tumors. ctDNA based techniques are able to detect the emergence of drug resistance mechanisms with high sensitivity and prior to radiological progression (12-14). This technique might identify drug resistant clones before subclonal resistance (resistance of the new clone to targeted treatment) develops and allow to eliminate the new clone with short-term additional treatment, while continuing treatment of the main oncogenic driver (EGFR exon 19 del / exon 21 L858R) with the EGFR TKI. Continuous ctDNA based monitoring will reveal the success of the additional treatment and in case the follow-up ctDNA sample shows elimination of the EGFR TKI resistant clone, the add-on treatment will be discontinued. Continuous ctDNA based monitoring might identify a new resistant clone at a later point in time and temporary treatment of this clone can be initiated. The EGFR TKI will remain the backbone of therapy and will not be discontinued (see treatment strategy 1 in Figure 3). This continuous track and treat strategy could potentially lead to a better outcome. In this study the investigators will track all known EGFR TKI resistance mechanisms over time and select one (MET amplification) for the track and treat strategy. Treatment strategy 1: Track and treat strategy. ctDNA based resistance monitoring. As soon as a resistant clone is detected with ctDNA, treatment will be added to the EGFR TKI. ctDNA will be continuously screened for resistant clones. Upon disappearance of the resistant clone, add-on treatment will be discontinued, while the EGFR TKI will be continued at any time. Multiple resistance mechanisms can be treated serially. Treatment strategy 2: routine care. Treatment with an EGFR TKI will be continued until radiological progression.