Genotyping of cerebrospinal fluid for leptomeningeal metastases in EGFR-mutated lung cancer

Abstract

Background: Leptomeningeal metastasis (LM) is a detrimental complication of advanced lung cancer, more frequently occurring in patients harboring epidermal growth factor receptor (EGFR) mutation. Due to limited access to the leptomeningeal lesion, we explored the potential role of cerebrospinal fluid (CSF) as a source for liquid biopsy in LM patients with EGFR mutation.Materials and methods: The CSF samples from Lung cancer patients with LM were collected between June 2021 and August 2018 at First Affiliated Hospital of Zhengzhou University. Next-generation sequencing was performed to detect the mutations in EGFR genes, overall 38 patients detected with EGFR mutations were finally enrolled in further retrospectively clinical analyses.Results: CSF samples of 38 lung patients with LM harboring EGFR mutation were enrolled in this study.we found 20 cases of L858R of exon 21 and 14 cases of exon 19 deletion.Other EGFR mutations included EGFR exon 20 insertion(n=1),EGFR G719A of exon 18 (n=1) ,EGFR G719S of exon 18 (n=1), EGFR S768I of exon 20 and G719C of exon 18(n=1).CSF samples from 6 patients were collected before prescribing them TKIs.The most frequently detected concurrent genes in CSF was TP53 missense mutation(50%).CSF of 10 patients were obtained after failure to 1st TKI.The most frequently detected concurrent genes in CSF were TP53 missense mutation(40%,n=4),EGFR copy number amplification (40%,n=4) and NKX2-1 copy number gain(30.0%,n=3).Acquired resistance to 1st TKI of T790M mutation was detected in two patients. Similarly, the CSF samples from 22 patients were collected during their 3rd TKI therapy and the TP53 missense mutation was detected in 31.8% of patients followed by EGFR amplification (22.7%), STK11 deletions (18.2%) and MYC amplification (18.2%), while two patients harbored T790M mutation. Known mechanisms of acquired resistance to EGFR- 3rd TKIs were identified in 31.8% of cases. C797S and C797G mutation was found in three patients.Possible EGFR-independent resistant mechanism included PIK3CA missense mutation(4.5%),MET amplification(4.5%),CDK4 amplification(4.5%) and RET gene fusion(4.5%).In the 38 cases , average TMB was 8.4mutations/Mb (median 6.9 , range 1.1-23.83mutations/Mb) ,12 cases with more than 10 mutations/Mb. There were no significant difference of CSF TMB among the three group of patients who hadn’t received TKI, progressed on 1st TKI and progressed on 3rd TKI.Conclusion: CSF cfDNA provided comprehensive profiles of driver and resistance genes of lung cancer with LM harboring EGFR mutation, supporting the importance of CSF cfDNA as a liquid biopsy medium and guiding the choice of anti-tumor drugs.