194eP Large-panel diagnostics detect heterogeneous alterations in acquired resistance to targeted NSCLC treatment

Background: Acquired resistance and progressive disease are inevitable in patients with non-small cell lung cancer (NSCLC) who are undergoing targeted therapy for driver mutations.However, the small size of the panels used to identify resistance mechanisms often prevents the detection of potentially targetable resistance mutations.We performed massive-parallel sequencing (MPS) to study resistance to targeted therapy. Methods:We analyzed samples from patients with advanced NSCLC who had progressed on targeted therapy using TrueSight Oncology 500 (TSO 500) sequencing.The dataset consists of patients presented at the molecular tumorboard (MTB) at the Center for Integrated Oncology Cologne.Results: From January to December 2025, 77 patients were analyzed.30 patients were excluded.Nearly all of the patients in this analysis (n=47) had adenocarcinoma histology (n = 40, 85.1% ).Most patients were female (n=33, 70.2%), with a median age of 57 years (range, 23-83) and an ECOG performance status of 0 (range, 0-3).Never-smokers represented 8 out of 25 patients with known smoking status.The most common driver alterations were EGFR mutations (n=27; 57.4%), followed by ALK rearrangements (n=7, 14.8%) and KRAS G12C mutation (n=5, 10.6%).MET amplification was the most common mode of resistance (n=8/27 in the EGFR group, n=3/7 with ALK fusion).We detected mutations and loss of function of the cell-cyclecontrolling genes CDKN2A, CDKN2B and mutations in RB1 in 7 patients with and without EGFR mutations.Notably, BRAF V600E mutations were acquired in two EGFR patients, and one acquired EML4::ALK V3 fusion was detected in a patient with EGFR exon 19del.Typical on-target mutations could be identified in the ALK, ROS1, and EGFR cohort.Conclusions: Analyzing targeted treated NSCLC patients with a larger sequencing approach reveals many potential modes of acquired resistance.Further work on the detected variants of unknown significance is ongoing.