Progressive <i>ROS1</i> Fusion-positive Non-small-cell Lung Cancer with Multiple Endobronchial Metastases: A Case Report

A 61-year-old man with no smoking history was admitted to our hospital with severe respiratory failure. Chest computed tomography revealed a mass in the right lung lobe with bilateral pulmonary dissemination and bronchial wall thickening. Bronchoscopy showed multiple endobronchial nodules, and histopathological examination confirmed adenocarcinoma. The patient was diagnosed with stage IV non-small-cell lung cancer (NSCLC), and despite poor performance status, platinum-based doublet chemotherapy was administered. After the first cycle, ROS1-positive adenocarcinoma was documented and treatment switched to crizotinib. The patient was diagnosed with stage IVA ROS1-positive NSCLC with pulmonary and endobronchial metastases (EBM). Despite poor condition, chemotherapy was initiated, followed by crizotinib. The patient's symptoms were alleviated; EBM disappeared on follow-up bronchoscopy, and he returned to work. Progression-free survival was maintained for 17 months until asymptomatic brain metastases developed. EBM is rare in NSCLC, particularly uncommon in ROS1-positive cases, and more frequently observed in NSCLC with EGFR or EML4-ALK mutations. This case suggests that ROS1-positive NSCLC may exhibit unique metastatic patterns. To our knowledge, this is the first reported case of ROS1 fusion-positive NSCLC presenting with EBM at the time of diagnosis.