EGFR mutation status in cerebrospinal fluid of NSCLC patients who developed leptomeningeal metastasis after EGFR-TKI treatment.

8081 Background: Prognosis for these patients with leptomeningeal metastasis (LM) is very poor due to the lack of therapeutic options. It was suggested that the leptomeningeal space is protected from the systemic chemotherapy as well as EGFR-TKIs. Therefore, it would be interesting to explore the EGFR mutation status in CSF of the NSCLC patients who developed LM after the initial response to EGFR-TKI. In this study, we attempted to address two questions: 1. what is the EGFR mutation status in CSF of this group of patients? 2. what is the difference of EGFR mutation status in CSF as compared to that in the concurrent plasma samples? Methods: A highly sensitive droplet digital PCR (ddPCR) method was used to detect EGFR mutation in 7 CSF samples which were collected from seven patients with NSCLC who initially responded to EGFR-TKI and developed LM afterwards. Concurrent plasma samples were collected and analyzed as well for comparison. Results: EGFR-sensitive mutations were detected in CSF of all 7 patients...