Integrating real-time in vivo tumour genomes for longitudinal analysis and management of glioma recurrence

Dear Editor, Tumour recurrence is the leading cause of glioma mortality. Current therapies based on excised tumour tissues cannot be lastingly effective due to the waning representativeness of in vitro primary tumours for the in vivo glioma caused by the spatiotemporal heterogeneity. Therefore, real-time in vivo genomic information of the tumour is needed for precisionmanagement and longitudinal analysis of glioma recurrence. We here evaluated the clinical applicability of glioma-derived circulating tumour DNA (ctDNA) from cerebrospinal fluid (CSF) and tumour in situ fluid (TISF), the latter denoting the fluid within surgical cavities,1 and proposed the CSF-tumour tissue-TISF (CTT) sequencing pattern that allows in vivo real-time genomic profiling of glioma during the clinical course. We detected ctDNA in TISF from 36 of 36 (100%) patients during their post-operative courses. These gliomas covered different subtypes, locations and progression stages (0.3-42.4 months after primary surgery) (Table S1). Importantly, we found that variant allele fractions (VAFs) of TISF ctDNA increased with tumour progression, even when the process is beyond imaging modalities (Figure 1A, Figure S1A,B). Moreover, the TISF ctDNA detected before postoperative anti-tumour treatment probably mirrored the molecular residue and complemented tumour tissues for the spatial architecture of the genome of primary gliomas (Figure 1B). Tumour-derived genetic mutations were identified in 18 of 34 CSF samples (54.5%) from 33 patients (Table S2). In our cohort, detectable CSF ctDNA was associated with radiographic features including tumour progression (p = 0.0048) and tumour touching the CSF space (p < 0.005) (Figure 1C,D). CSF ctDNA was especially insensitive to post-operative gliomas without radiographic progression (0/9, 0%, Figure 1D). Similarly, Miller et al previously reported that shedding tumour DNA into the CSF was related to tumour progression, tumour burden and tumour spreading towards the CSF circulating system.2