Researchers have announced promising results for a new targeted therapy called zidesamtinib, which showed a 94% response rate in patients with a rare type of non-small cell lung cancer. This cancer is defined by a specific genetic abnormality known as ROS1 gene fusion. The findings were presented at the World Conference on Lung Cancer 2026 (WCLC) and come from the ARROS-1 trial, an international phase I/II study involving 94 patients with advanced ROS1-positive lung cancer who had not previously been treated with a class of drugs called tyrosine kinase inhibitors. These patients took 100 milligrams of zidesamtinib once daily. Among them, 88 experienced an objective response, meaning their tumors shrank or disappeared partially, with 15% achieving a complete response, where tumors disappeared entirely on imaging scans. The benefits of the treatment appeared to last over time, with 86% of responders still benefiting after one year, and 90% not seeing their condition worsen. The average time the patients were followed was 15.2 months, though researchers have not yet determined how long the treatment effects will last for half of the patients. A major challenge in treating ROS1-positive lung cancer is its tendency to spread to the central nervous system, particularly the brain. However, zidesamtinib showed effectiveness in this area. Among 10 patients with measurable brain metastases at the start of the study, all achieved an intracranial response, meaning the drug helped shrink or control the brain tumors. Of these, 70% had a complete response in the brain, and 78% of these responses were still present after 12 months. Additionally, no worsening of the central nervous system was observed in the 78 patients who did not have brain metastases at the start of the study. Despite the positive outcomes, zidesamtinib is not without side effects. The most commonly reported were peripheral edema, or swelling in the arms and legs, affecting 34% of patients, as well as weight gain, increased levels of certain enzymes in the blood, and changes in taste. These side effects caused 11% of patients to reduce their dose and 1% to stop the treatment entirely. Dr. Alexander Drilon, who led the study and is director of the Early Drug Development Service at Memorial Sloan Kettering Cancer Center, called the durable responses and low discontinuation rates a promising development. However, zidesamtinib is currently approved by the FDA only for patients who have already received a first anti-ROS1 treatment. Its use as a first-line treatment is not yet approved and will require further confirmation from long-term data. The results should be interpreted with caution, as the ARROS-1 trial did not include a control group for comparison, and the data presented at the conference have not yet been published in a peer-reviewed journal. Additionally, the subgroup of patients with brain metastases was very small, only 10 individuals. While the high response rate is encouraging, it does not provide definitive evidence about the drug’s effect on overall survival or whether it is more effective than existing treatments.