The ROS1 tyrosine kinase is activated through ROS1 gene rearrangements in 1% to 2% of non–small-cell lung cancers (NSCLCs), which confer sensitivity to treatment with the anaplastic lymphoma kinase (ALK)/ROS1/mesenchymal-epithelial transition factor inhibitor crizotinib. Currently, insights into patterns of metastatic spread and mechanisms of crizotinib resistance among patients with ROS1-positive disease are limited.

We reviewed clinical and radiographic imaging data of patients with ROS1- and ALK-positive NSCLC to compare patterns of metastatic spread at initial metastatic diagnosis. To determine molecular mechanisms of crizotinib resistance, we analyzed repeat biopsy specimens from a cohort of patients with ROS1-positive disease who progressed on crizotinib.

We identified 39 and 196 patients with advanced ROS1- and ALK-positive NSCLC, respectively. Patients with ROS1-positive disease had significantly lower rates of extrathoracic metastases (ROS1, 59.0%; ALK, 83.2%; P = .002), including lower rates of brain metastases (ROS1, 19.4%; ALK, 39.1%; P = .033), at initial metastatic diagnosis. Despite similar overall survival between patients with ALK- and ROS1-positive NSCLC treated with crizotinib (median, 3.0 v 2.5 years, respectively; P = .786), patients with ROS1-positive NSCLC also had a significantly lower cumulative incidence of brain metastases (34% v 73% at 5 years; P < .001). In addition, we identified 16 patients who underwent a total of 17 repeat biopsies after progression on crizotinib. ROS1 resistance mutations were identified in 53% of specimens, including nine (64%) of 14 non–brain metastasis specimens. ROS1 mutations included G2032R (41%), D2033N (6%), and S1986F (6%).

Compared with ALK rearrangements, ROS1 rearrangements are associated with lower rates of extrathoracic metastases, including fewer brain metastases, at initial metastatic diagnosis. ROS1 resistance mutations, particularly G2032R, appear to be the predominant mechanism of resistance to crizotinib, which underscores the need to develop novel ROS1 inhibitors with activity against these resistant mutants.