Spectrum of Mechanisms of Resistance to Crizotinib and Lorlatinib in ROS1 Fusion-Positive Lung Cancer.

Purpose Current standard initial therapy for advanced, ROS1 fusion-positive (ROS1+) non-small cell lung cancer (NSCLC) is crizotinib or entrectinib. Lorlatinib, a next-generation ALK/ROS1 inhibitor, recently demonstrated efficacy in ROS1+ NSCLC including in crizotinib-pretreated patients. However, mechanisms of lorlatinib resistance in ROS1+ disease remain poorly understood. Here, we assessed mechanisms of resistance to crizotinib and lorlatinib. Experimental design Biopsies from ROS1+ NSCLC patients progressing on crizotinib or lorlatinib were profiled by genetic sequencing. Results From 55 patients, 47 post-crizotinib and 32 post-lorlatinib biopsies were assessed. Among 42 post-crizotinib and 28 post-lorlatinib biopsies analyzed at distinct timepoints, ROS1 mutations were identified in 38% and 46%, respectively. ROS1 G2032R was the most common occurring in approximately a third of cases. Additional ROS1 mutations included: D2033N (2.4%) and S1986F (2.4%) post-crizotinib; L2086F (3.6%), G2032R/L2086F (3.6%), G2032R/S1986F/L2086F (3.6%), and S1986F/L2000V (3.6%) post-lorlatinib. Structural modeling predicted ROS1L2086F causes steric interference to lorlatinib, crizotinib, and entrectinib, while it may accommodate cabozantinib. In Ba/F3 models, ROS1L2086F, ROS1G2032R/L2086F, and ROS1S1986F/G2032R/L2086F were refractory to lorlatinib but sensitive to cabozantinib. A patient with disease progression on crizotinib and lorlatinib and ROS1 L2086F received cabozantinib for nearly 11 months with disease control. Among lorlatinib-resistant biopsies, we also identified MET amplification (4%), KRAS G12C (4%), KRAS amplification (4%), NRAS mutation (4%), and MAP2K1 mutation (4%). Conclusions ROS1 mutations mediate resistance to crizotinib and lorlatinib in over one-third of cases, underscoring the importance of developing next-generation ROS1 inhibitors with potency against these mutations including G2032R and L2086F. Continued efforts are needed to elucidate ROS1-independent resistance mechanisms.