A Study of the Safety and Efficacy of Pemetrexed Combined with Nivolumab Via Intraventricular Injection for the Treatment of Refractory Non-squamous Non-small Cell Lung Cancer with Leptomeningeal Metastases

This study is testing whether injecting chemotherapy drugs (pemetrexed) and an immunotherapy drug (nivolumab) directly into the fluid-filled spaces around the brain and spine can treat non-small cell lung cancer (non-squamous type) that has spread to the lining of the brain (leptomeningeal metastases). **You may be eligible if...** - You have confirmed non-small cell lung cancer with leptomeningeal disease (cancer spread to the brain/spine lining), confirmed by imaging or spinal fluid analysis - Your overall health status is ECOG 2 or better - Your neurological symptoms are stable - You are willing to undergo spinal fluid sampling (lumbar puncture) **You may NOT be eligible if...** - You have blockage of spinal fluid circulation in the brain - You have serious blood clotting problems or are on anticoagulants that cannot be adjusted - You have severe organ dysfunction - You are pregnant or breastfeeding Talk to your doctor to see if this trial is right for you.