Intrathecal Pemetrexed for Leptomeningeal Metastasis in EGFR-Mutant NSCLC

Leptomeningeal metastasis (LM) is a complication of advanced non-small cell lung cancer (NSCLC). The incidence of LM in NSCLC patients is around 3-5 %, reaching 9.4 % of those with an epidermal growth factor receptor (EGFR) mutation. Generally, the efficacy of systemic treatment for LM is limited due to the blood-brain barrier. Osimertinib has a high central nervous system penetration rate, making it the preferred first-line treatment for EGFR-mutant NSCLC. Previous studies indicated that osimertinib had shown promising efficacy in pretreated patients harboring EGFR mutations and LM. However, intracranial disease progression eventually develops, and the prognosis of patients with LM progression after osimertinib is poor. Recently, intrathecal chemotherapy with pemetrexed (IP) was reported to be an alternative treatment in patients with NSCLC and LM. The results from a phase I/II trial examining the efficacy and safety of IP in patients with EGFR-mutant NSCLC after the failure of previous TKI, and 83% of study enrollees received osimertinib before IP. The clinical response rate was 84.6%, and the median overall survival was 9.0 months. Despite initial promising efficacy, further trials are needed to verify these results. Therefore, the investigators plan to conduct a prospective study to examine the safety and effectiveness of IP combined with EGFR-TKI for patients with EGFR mutant NSCLC after osimertinib failure.