Tissue Biopsy | Liquid Biopsy |
---|---|
Requires invasive procedure | Minimally invasive |
Unable to capture tumour heterogeneity | Overcomes challenges of tumour heterogeneity |
Unable to assess temporal genomic changes | Real time genomic monitoring and cancer evolution monitoring |
Very low risk of false positives (CHIP) | Risk of false positives (CHIP) |
Risk of non-diagnostic sample | Variable detection rate (dependant on stage, site of metastases, type of cancer) |
Technical consideration for tissue processing required (storage of tissue, cutting, histopathological review) | Pre-analytical va |
Technology | Example | Molecular Targets | Detection Limit | Limitations | Benefits |
---|---|---|---|---|---|
Allele-Specific PCR Assay | Roche/Cobas | Known mutations | <0.01% | Only semi-quantitative; less sensitive compared with ddPCR | Highly specific with broad coverage |
Emulsion PCR Assays | ddPCR BEAMing | Known mutations | <0.01% | Less specific. Unable to detect CNV/fusions | Fully quantitative |
Targeted NGS Assays |
Amplicon-based | TAM-Seq | Hotspot SNV and CNV | <0.1% | Less sensitive and limited variant analysis compared to capture-based assay | Fast and cost effective |
Capture-based | Guardant360© | SNV, CNV, fusions | <0.1% | Lower specificity compared to amplicon-based assays, complex, and slower. | Higher sensitivity compared with amplicon sequencing |
Non-targeted NGS Assays | Whole-genome sequencing Whole-exome sequencing | All variants | <1% | Reduced sequencing depth compared with NGS, costly | Genome-wide analysis |
Wow very high detection rate 39% just by using blood vs 54% using tissue. Very good!2. ctDNA Detection in Gastric Cancer
ctDNA can be detected in individuals with early- and late-stage GC. A study using a plasma-based, whole-genome NGS panel in 44 patients with any stage gastric (n = 39) and oesophageal cancer (n = 5) revealed a ctDNA detection rate of approximately 39%, with a VAF range of 2.5–8%. Interestingly, the concordance with tissue was only 54% [33]. Another study of 29 patients with any stage GC showed a ctDNA detection rate of 91.3% using a targeted NGS panel, with a VAF ranging from 2.8% to 87.1% and an average of 5.4 somatic variants detected per patient. The tissue concordance was 47.8% in this cohort. Even small tumours such as T1-T2 shed ctDNA [34].
genomic alterations,
MSI prevalence
PIK3CA mutation
CCNE1 amplification (20%)