Prognostic value of cell-free DNA in cerebrospinal fluid from lung cancer patients with brain metastases during radiotherapy

Abstract

Background: During the last decades, radiotherapy (RT) for non-small cell lung cancer (NSCLC) with brain metastases (BM) has been developed. However, the lack of predictive biomarkers for therapeutic responses has limited the precision treatment in NSCLC-BM.

Patients and methods: In order to find the predictive biomarkers for RT, we investigated the influence of RT on the cell-free DNA (cfDNA) from cerebrospinal fluid (CSF) and the frequency of T cell subsets of NSCLC patients with BM. A total of 19 patients diagnosed as NSCLC with BM were enrolled. The CSF from 19 patients and matched plasma samples from 11 patients were collected before RT, during RT, and after RT. The cfDNA from CSF and plasma were extracted, and the cerebrospinal fluid tumor mutation burden (cTMB) was calculated after through next-generation sequencing. The frequency of T cell subsets in peripheral blood was using flow cytometry.

Results: The detection rate of cfDNA was higher in CSF compared to plasma in the matched samples. The mutation abundance of cfDNA in CSF was decreased after RT. However, no significant difference was observed in cTMB before and after RT. Although the median intracranial progression-free survival (iPFS) has not yet been reached in patients with decreased or undetectable cTMB, there was a trend that these patients possessed longer iPFS compared to those with stable or increased cTMB (HR 0.28, 95% CI 0.07-1.18, P = 0.067). The proportion of CD4⁺T cells in peripheral blood was decreased after RT.

Conclusion: Our study indicates that cTMB can serve as a prognostic biomarker in NSCLC patients with BMs.

Keywords: Brain metastases; Cell-free DNA; NSCLC; Radiotherapy; cTMB.

Fig. 1

The amount of CSF cfDNA. A CSF cfDNA of patients D01-D08 collected at 0 day (baseline), 7th day and 10th day (during RT therapy), 20th day (after RT therapy) since the RT therapy began. B CSF cfDNA of patients S01–S11 collected at 0 day (baseline), 10th day (during RT therapy), 20th day (after RT) since the RT therapy began. RT radiation therapy

Fig. 2

A The cfDNA detection rate of CSF and plasma. RT radiation therapy, CSF cerebrospinal fluid. B Genomic mutations abundance from the CSF. C1 before RT, C2 during RT, and C3 after RT. RT radiation therapy, CSF cerebrospinal fluid

Fig. 3

Genomic alterations in the CSF of training cohort at different timepoint. INDEL insertion-deletion, CNV copy number variation, CSF Cerebrospinal Fluid, RT radiation therapy

Fig. 4

A Cerebrospinal fluid TMB change of cohort before RT, during RT, and after RT. No significant difference was observed. CSF cerebrospinal fluid, TMB tumor mutation burden, RT radiation therapy, ns: no significance. B Kaplan–Meier curves of intracranial progression free survival (iPFS) comparing cerebrospinal fluid TMB decrease/undetectable and TMB increase/no change. C Plasma TMB change before RT, during RT, and after RT. No significant difference was observed. TMB tumor mutation burden, RT radiation therapy, ns no significance