Leptomeningeal Metastasis From Lung Cancer

\*\*Brief Summary (English)\*\* The goal of this clinical trial is to learn if a risk-adaptive consolidation therapy, guided by cerebrospinal fluid (CSF) circulating tumor DNA (ctDNA) clearance kinetics after induction intrathecal pemetrexed, can improve intracranial progression-free survival (iPFS) compared to standard intrathecal pemetrexed consolidation in patients with leptomeningeal metastasis (LM) from EGFR-mutant non-small cell lung cancer (NSCLC) that has progressed on third-generation EGFR-TKIs. It will also learn about the safety and tolerability of proton craniospinal irradiation (pCSI) in this setting. The main questions it aims to answer are: * Does risk-adaptive consolidation therapy (pCSI with or without concurrent low-dose intrathecal pemetrexed) prolong iPFS compared to standard intrathecal pemetrexed consolidation? * What medical problems do participants have when receiving pCSI or intrathecal pemetrexed? Researchers will compare the experimental arm (risk-adaptive consolidation: pCSI for intermediate-risk, or pCSI with concurrent low-dose intrathecal pemetrexed for high-risk patients) to the control arm (standard intrathecal pemetrexed consolidation) to see if the adaptive strategy improves survival outcomes. Participants will: * Receive induction intrathecal pemetrexed (40 mg, biw, q3w for 2 cycles) via Ommaya reservoir. * Undergo CSF collection at baseline and after induction for ctDNA (maxVAF) analysis to determine risk stratification (low, intermediate, high). * If stratified as intermediate or high risk, be randomly assigned to either standard intrathecal pemetrexed consolidation or risk-adaptive consolidation (pCSI 30 GyE/10f for intermediate-risk; pCSI 30 GyE/10f with concurrent intrathecal pemetrexed 30 mg on d1, d8 for high-risk). * Receive maintenance intrathecal pemetrexed (40 mg, q4w) until intracranial progression. * Undergo regular efficacy assessments (contrast-enhanced MRI of brain and whole spine) every 8 weeks, and complete neurocognitive and quality-of-life questionnaires.

The goal of this clinical trial is to learn whether amivantamab combined with intrathecal pemetrexed is safe and may help treat leptomeningeal metastasis in adults with EGFR-mutant lung adenocarcinoma. Leptomeningeal metastasis occurs when cancer cells spread to the membranes surrounding the brain and spinal cord or to the cerebrospinal fluid. It is a serious complication of advanced lung cancer and is difficult to treat because many systemic drugs do not reach high enough levels in the cerebrospinal fluid. The main questions this study aims to answer are: What medical problems do participants have when receiving amivantamab combined with intrathecal pemetrexed? How long do participants live without their disease getting worse after receiving this treatment? How long do participants survive after starting this treatment? Participants will: Receive amivantamab by intravenous infusion according to the study schedule. Receive intrathecal pemetrexed, together with dexamethasone and normal saline, once every week. Continue their original EGFR tyrosine kinase inhibitor treatment as determined by the study doctor. Have cerebrospinal fluid pressure measured and cerebrospinal fluid samples collected before each intrathecal treatment. Have tests of cerebrospinal fluid, including routine tests, biochemical tests, tumor markers, albumin, IgG, and cytology. Have imaging tests, including enhanced MRI, about every 3 months to check the disease. Be followed by clinic visits and/or telephone calls to collect information about survival, disease status, side effects, and any later cancer treatments.

This is a phase I/II, single-arm, open-label, single-center clinical trial to evaluate the safety, tolerability, and preliminary efficacy of intrathecal injection of methotrexate-loaded autologous tumor cell-derived microparticles (MTX-MPs) in patients with leptomeningeal metastasis from lung cancer who have failed standard of care. The study consists of two phases: Phase I employs an accelerated titration combined with a "3+3" dose-escalation design to determine the maximum tolerated dose (MTD) and the recommended phase II dose (RP2D). Phase II further assesses the objective response rate (ORR) at the RP2D. Key secondary endpoints include progression-free survival (PFS), overall survival (OS), and safety profile. Approximately 10-20 patients with cytologically confirmed leptomeningeal metastasis (age ≥18 years, ECOG PS 0-3) will be enrolled. Participants will receive intrathecal MTX-MPs on days 1, 3, and 5 of the first cycle, followed by once every 3 weeks (Q3W) until disease progression, unacceptable toxicity, or death. Tumor response will be evaluated using the Response Assessment in Neuro-Oncology (RANO) criteria for leptomeningeal metastasis, and adverse events will be graded according to CTCAE version 5.0. This exploratory study may provide a novel local therapeutic approach for leptomeningeal metastasis from lung cancer.