LAUSR

INTRODUCTION ROS1-rearranged non-small cell lung cancer (NSCLC) has demonstrated promising response to lorlatinib; however, no targeted therapy is available after failure of lorlatinib and information on acquired resistance mechanisms mediating lorlatinib resistance among ROS1-rearranged NSCLC patients is limited. We report a ROS1-rearranged NSCLC patient who responded to immunochemotherapy after acquisition of ROS1 G2032K-mediated lorlatinib resistance. METHODS Next-generation sequencing (NGS) was performed on supraclavicular lymph nodes (SLN) and blood samples obtained from the 53-year old male patient with advanced CD74-ROS1-rearranged NSCLC. In vitro experiments with patient-derived SLN tumor cells and in silico homology modeling were performed to investigate mechanisms of G2032K-mediated inhibitor resistance. RESULTS NGS analysis revealed the detection of an acquired ROS1 G2032 K after failure from lorlatinib. Homology modeling revealed the conformational change in the inhibitor binding site induced by the ROS1 G2032 K that disrupted lorlatinib binding. In vitro experiments using patient-derived cells bearing concurrent CD74-ROS1-rearrangement and ROS1 G2032 K demonstrated half-maximal inhibitory concentration IC50 of 730.2 nM for lorlatinib, 812.1 nM for entrectinib, and 1546 nM for crizotinib, indicating resistance to these inhibitors. With PD-L1 expression of TPS 30 %, nab-paclitaxel plus pembrolizumab was administered as fifth-line treatment and achieved partial response, with sustained response ongoing for 7 months as of January 31, 2020. CONCLUSION ROS1 G2032 K is a novel mutation that mediates resistance to lorlatinib. With the lack of targeted therapeutic options after lorlatinib resistance, checkpoint inhibitor plus chemotherapy may be considered as a treatment option in patients with ROS1-rearranged NSCLC.