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

Purpose: Current standard initial therapy for advanced, ROS proto-oncogene 1, receptor tyrosine kinase fusion ()-positive (ROS1) non-small cell lung cancer (NSCLC) is crizotinib or entrectinib. Lorlatinib, a next-generation anaplastic lymphoma kinase/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 patients with ROS1 NSCLC 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, mutations were identified in 38% and 46%, respectively. G2032R was the most commonly occurring mutation in approximately one third of cases. Additional mutations included D2033N (2.4%) and S1986F (2.4%) post-crizotinib and L2086F (3.6%), G2032R/L2086F (3.6%), G2032R/S1986F/L2086F (3.6%), and S1986F/L2000V (3.6%) post-lorlatinib. Structural modeling predicted ROS1 causes steric interference to lorlatinib, crizotinib, and entrectinib, while it may accommodate cabozantinib. In Ba/F3 models, ROS1, ROS1, and ROS1 were refractory to lorlatinib but sensitive to cabozantinib. A patient with disease progression on crizotinib and lorlatinib and L2086F received cabozantinib for nearly 11 months with disease control. Among lorlatinib-resistant biopsies, we also identified amplification (4%), G12C (4%), amplification (4%), mutation (4%), and mutation (4%).

Conclusions: mutations mediate resistance to crizotinib and lorlatinib in more than 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.