CAPP-seq analysis of circulating tumor DNA from patients with EGFR T790M-positive lung cancer after osimertinib.

We here applied cancer personalized profiling by deep sequencing (CAPP-seq) to analysis of circulating tumor DNA (ctDNA) to identify resistance mechanisms in osimertinib-treated patients with EGFR T790M–positive non–small cell lung cancer (NSCLC). The study included patients with EGFR activating mutation–positive advanced NSCLC who were positive for T790M in tumor tissue or plasma after previous treatment with an EGFR tyrosine kinase inhibitor, who received osimertinib at Kindai University Hospital between August 2014 and September 2017, and for whom plasma collected after progression on osimertinib was available. Clinical data were extracted from medical records. Patients with innate resistance to osimertinib were defined as those whose best response was progressive disease or stable disease for   6 months were considered as having acquired resistance. We performed CAPP-seq for 20 patients at progression on osimertinib. Distinct patterns of genomic alterations were apparent in patients with innate versus acquired resistance. Mutations in PIK3CA, KRAS, or BRAF and copy number gain for EGFR, ERBB2, or MET were more common in patients with innate resistance than in those with acquired resistance. In addition, one patient who underwent a repeat biopsy was found to harbor the C797S mutation of EGFR after disease progression during osimertinib rechallenge, with this mutation not having been detected at the time of initial progression on osimertinib. CAPP-seq analysis of ctDNA was able to identify potentially targetable genetic alterations in patients with osimertinib resistance.