Study on the Mechanism of Acquired Resistance of Entrectinib

This study is investigating what causes resistance to entrectinib — a targeted therapy for non-small cell lung cancer with a ROS1 gene fusion — after it initially works. Researchers want to identify the biological changes that allow the cancer to start growing again, to guide future treatment strategies. **You may be eligible if...** - You are 18 or older with advanced non-small cell lung cancer (stage IIIB–IV) - Your cancer has a ROS1 gene fusion confirmed by molecular testing - You have not previously received systemic treatment for your advanced-stage cancer - You have at least one measurable tumor on imaging **You may NOT be eligible if...** - You have already been treated with systemic chemotherapy, immunotherapy, or targeted drugs for your advanced-stage disease - Your cancer does not have a confirmed ROS1 fusion - You do not have measurable disease Talk to your doctor to see if this trial is right for you.