Single center, open and prospective evaluation of genomic sequencing on cerebro-spinal fluid, brain metastatic lesions and plasma from patients in non-small cell lung cancer with brain metastasis.

e13578 Background: Leptomeningeal metastases are observed in 9.4% non–small Cell Lung Cancer (NSCLC) patients with EGFR mutations. Depending on patient specific gene mutations, tumor cells may also have different proliferative activity, leading to differential metastatic potential. However, the clinical significance of observed gene mutation differences between CSF, plasma, primary pulmonary tumor and metastatic brain tumor samples remains unclear and should be further explored. Methods: From Apr. 2018 to Jan. 2019, plasma and CSF paired samples were drawn from consented NSCLC patients with diagnosed brain metastasis. Of these 21, brain lesion samples were obtained from 5 patients. All the samples were tested by next-generation sequencing. Patients were treated based on the detection results. Results: For this cohort, the detection rate of EGFR mutations in CSF cfDNA versus plasma cfDNA/CTC was 57.1% and 23.8% respectively (p < 0.05). For patients who had not received tyrosine kinase inhibitor (TKI) therapy, the CSF cfDNA EGFR mutation results were consistent with results for plasma, brain lesion and primary tumor samples. Conversely, for patients who had received TKI therapy, EGFR mutations detected in CSF were consistent with those from brain samples, but different from those observed in plasma or primary tumor samples. A high response rate (ORR, 70%; DCR, 90%) was observed in patients with EGFR positive detected in CSF after treatment with second orthird-generation TKI. Among the EGFR mutations detected in CSF, the EGFR uncommon mutation frequency was 58.3%(7/12), including G7I9A/L861Q/L703P/R776H/G575R/T790M 85.7% (6/7) of these occurred in LM patients. One patient who progressed from BM to LM had an uncommon mutation in the CSF sample. Among these five patients with EGFR G719A or L861Q positive and T790M negative, 4 patients had PR and 1 patient had SD after the second-generation TKI therapy. Conclusions: Differences in EGFR gene mutations were observed between CSF, plasma, primary pulmonary lesion and brain tissue samples in NSCLC patients with diagnosed brain metastasis after TKI therapy. The reasons for this discrepancy remain to be understood. Nevertheless, CSF may be a useful prognostic tool for patient monitoring and metastasis risk evaluation. The detection of uncommon EGFR mutations may increase the risk of LM in NSCLC patients. Clinical trial information: ChiCTR1800017499.