The Impact of Leptomeningeal Metastasis in Patients with Non-Small Cell Lung Cancer with EGFR Mutation: Survival Analysis of a Retrospective Cohort Study

Background: In metastatic non-small cell lung cancer (NSCLC) with epidermal growth factor receptor (EGFR) mutation, osimertinib is the cornerstone treatment able to prolong overall survival (OS). Evidence around osimertinib being effective in leptomeningeal metastasis (LM) is scarce. Methods: We conducted a retrospective cohort study of patients with metastatic NSCLC-EGFR mutation treated with osimertinib at Sunnybrook Hospital. Results: We identified a total of 56 patients. Of these, 45 (79.4%) were never smokers, 53 (94.6%) had adenocarcinoma histology, and 26 (46.42%) had either the EGFR exon 21-L858R mutation or exon 19 deletion. The estimated median OS was 51 months (43.5–58.5). All eight patients with LM died during the study period. From the time of NSCLC diagnosis, the OS of patients without LM was 53 months (95% CI 47.2–58.7), and with LM was 21 months (95% CI 3.0–39), p = 0.001. However, the median OS from LM diagnosis was 2 months (95% CI, 1.0–26). Conclusions: In our population of patients with metastatic NSCLC-EGFR mutation who received osimertinib, there was a significant reduction in life expectancy in the group with LM. Patients who had advanced stage at diagnosis and were more likely to develop LM exhibited poorer survival compared to those who had early-stage cancer at diagnosis and developed metastases later on.