Table 1.

Pros and cons of different approaches employed for liquid biopsy in glioblastoma

Approach	Pros	Cons
CTCs	Information can be provided at the protein, DNA, and RNA levels	Only a few studies have been carried out by using brain tumor–derived CTCs CTCs are rare (one cell in 109 blood cells) [25, 31, 32]
ctDNA	Might provide a comprehensive view of the glioblastoma genome [40, 41, 42, 43, 44, 45, 46, 47] Higher ctDNA levels compared with CTC	Blood ctDNA of patients with primary brain tumor is low compared with other tumors that are able to transfer ctDNA fragments into blood [50, 51, 52, 53, 54] Short half‐life, <1.5 hour Improvement in sequencing technologies is necessary [50, 51, 52, 53, 54]
miRNAs	Extremely stable in biological fluids [90] Using sophisticated software (e.g., TargetScan) it is possible to correlate miRNAs with potential target genes [91]	Development of panels of validated miRNAS is necessary because of the uncertainties of the current findings [100, 101]
Extracellular vesicles	Easy detection Better source of nucleic acids for tumor molecular profiling as compared with cell‐free nucleic acids [121] Promising data, such as detection of the EGFRvIII deletion variant [129]	Possible presence of contaminants by current isolation methods

Abbreviations: CTC, circulating tumor cell; ctDNA, circulating tumor DNA; EGFRvIII, EGFR variant III; miRNA, microRNA.