Abstract 723: Genetic profiling of cerebrospinal fluid cfDNA from NSCLC patients with leptomeningeal metastases reveals EGFR-TKIs resistant mutations independent of extracranial lesions (cases series)
Authors: Wu Xi , Xing Puyuan , Shi Min , Guo Weihua , Xiao Jianping , Wan Jinghai , Li Junling 
Published: September 2020

Abstract
Background: Leptomeningeal metastases (LM), associated with poor survival, were much more frequent in NSCLC patients harboring EGFR mutations. While EGFR-TKIs therapy significantly increased overall survival, many patients inevitably develop acquired resistance to them, which was a big challenge for the treatment of NSCLC with LM. Recently, cerebrospinal fluid (CSF) cfDNA (cell free DNA) has been reported to be more representative of the genomic alterations of LM than plasma cfDNA. So exploring the mechanism of EGFR-TKIs resistance in LM by CSF cfDNA will be more easier and beneficial for NSCLC patients with LM. Here, we reported cases series, demonstrating the acquired resistance mutations to the EGFR-TKIs in LM were independent of those in extracranial lesions.
Methods: The 31 lung adenocarcinoma patients harboring EGFR mutations, who had been received at least 6 months of EGFR-TKIs treatment before diagnosis of LM, were enrolled. 10 ml of CSF and matched 10 ml peripheral blood were collected. Genomic barcoded DNA libraries were constructed using more than 20 ng of cfDNA from CSF or plasma and captured using probes from designed lung cancer panels. Mutations with allelic fractions of more than 0.1%, supported by more than 4 unique reads and not detected in germline DNA, were analysis in this study.
Results: Consistent with previous studies, all driver mutations in primary tumours were detected in CSF cfDNA, while only 56.8% of driver mutations could be detected in plasma cfDNA. Comparing the genetic profiles between CSF cfDNA and plasma cfDNA, we found that 3 EGFR-TKIs resistant mutations were detected in CSF cfDNA but not in plasma cfDNA. In patient P08, EGFR C797S (c.2389T&gt;A) mutation was only detected in CSF cfDNA. While in plasma, it was replaced by another type EGFR C797S (c. 2390G&gt;C) mutation in cis with T790M (c.2369C&gt;T). It suggested that the acquired resistance mutations to EGFR-TKIs in the LM and extracranial lesions developed independently. In patient P17, who were exposed to 1st/3ndEGFR-TKIs before LM, EGFR C797S (c.2390G&gt;C) mutation was only detected in CSF but not in plasma. Based on CSF unique EGFR C797S mutation, the patient switched to therapy with Bevacizumab in combination with Pemetrexed and had survived for more than 10 months. Patient P32 was diagnosed with LM during treatment of Afatinib. The EGFR T790M (c.2369C&gt;T) mutation was only detected in CSF but not in plasma. Even received Osimertinib treatment, the patient still died 3.5 months after diagnosis of LM.
Conclusions: During EGFR-TKIs treatment, the acquired resistance mutations in the LM for NSCLC patients were independent of those in extracranial lesions. All the data suggested that both genetic profiling of CSF cfDNA and plasma cfDNA were necessary for NSCLC patients with LM to make clinical decisions.
Citation Format: Xi Wu, Puyuan Xing, Min Shi, Weihua Guo, Jianping Xiao, Jinghai Wan, Junling Li. Genetic profiling of cerebrospinal fluid cfDNA from NSCLC patients with leptomeningeal metastases reveals EGFR-TKIs resistant mutations independent of extracranial lesions (cases series) [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 723.