This phase I/II trial characterized the tolerability, safety, and antitumor activities of unecritinib, a novel derivative of crizotinib and a multi-tyrosine kinase inhibitor targeting ROS1, ALK, and c-MET, in advanced tumors and ROS1 inhibitor-naive advanced or metastatic non-small cell lung cancer (NSCLC) harboringROS1rearrangements. Eligible patients received unecritinib 100, 200, and 300 mg QD, and 200, 250, 300, and 350 mg BID in a 3 + 3 design during dose escalation and 300 and 350 mg BID during expansion. Phase II trial patients received unecritinib 300 mg BID in continuous 28-day cycles until disease progression or unacceptable toxicity. The primary endpoint was the objective response rate (ORR) per independent review committee (IRC). Key secondary endpoints included intracranial ORR and safety. The ORR of 36 efficacy evaluable patients in the phase I trial was 63.9% (95% CI 46.2%, 79.2%). In the phase II trial, 111 eligible patients in the main study cohort received unecritinib. The ORR per IRC was 80.2% (95% CI 71.5%, 87.1%) and the median progression-free survival (PFS) per IRC was 16.5 months (95% CI 10.2, 27.0). Additionally, 46.9% of the patients who received recommended phase II dose of 300 mg BID experienced grade 3 or higher treatment-related adverse events. Treatment-related ocular disorders and neurotoxicity occurred in 28.1% and 34.4% of patients, respectively, but none was grade 3 or higher. Unecritinib is efficacious and safe for ROS1 inhibitor-naive patients withROS1-positive advanced NSCLC, particularly patients with brain metastases at baseline, strongly supporting that unecritinib should become one of the standards of care forROS1-positive NSCLC.ClinicalTrials.gov identifier: NCT03019276 and NCT03972189.