We aimed to evaluate the efficacy and safety of intrathecal pemetrexed (IP) for treating EGFR-mutant leptomeningeal metastases (LMs) from EGFR-mutant NSCLC.

Patients with EGFR-mutant NSCLC with LM who had failed tyrosine kinase inhibitors were recruited. The dose of IP was escalated from 15 mg to 80 mg using an accelerated titration design in a phase 1 study. The recommended dose (RD) determined in phase 1 was used in the phase 2 study. The primary end point was treatment efficacy measured as the clinical response rate. Overall survival and adverse events (AEs) were evaluated as secondary end points.

The RD observed in the phase 1 study was 50 mg pemetrexed. A total of 30 cases of LM-NSCLC were enrolled in the phase 2 study, including 14 males and 16 females. Four patients did not survive for 4 weeks and could not be evaluated for efficacy. The clinical response rate was 84.6% (22 of 26). The median overall survival of all patients was 9.0 months (n = 30, 95% confidence interval: 6.6-11.4 mo). Most AEs were mild, and the most frequent AE of any grade was myelosuppression (n = 9, 30%), which returned to normal after symptomatic treatment.

This study revealed that 50 mg pemetrexed is the RD which results in few AEs and a good response rate. IP is an effective treatment for patients with EGFR-mutant NSCLC-LM who had failed on tyrosine kinase inhibitor.