Liquid biopsy — detecting circulating tumour DNA from a simple blood draw
What is Liquid Biopsy?
Liquid biopsy is a non-invasive blood test that detects circulating tumour DNA (ctDNA), circulating tumour cells (CTCs), and tumour-derived exosomes shed by cancer cells into the bloodstream. Unlike conventional tissue biopsy, it requires only a blood draw — no surgery, no anaesthesia, no recovery time.
The GRAIL Galleri test, now available in selected Istanbul oncology centres, can detect signals from 50+ cancer types from a single tube of blood, often before symptoms appear. A landmark study in 2023 (PATHFINDER) showed the test has a positive predictive value of 38% — meaning when it signals cancer, it is confirmed in more than a third of cases.
Cancer cells constantly shed DNA fragments into the blood. These cell-free DNA fragments carry distinctive methylation patterns (epigenetic "fingerprints") that differ from normal cells. Next-generation sequencing algorithms analyse these patterns to identify the likely tissue of origin with high specificity.
Clinical Applications in Istanbul Today
- Treatment monitoring: Tracking ctDNA levels during chemotherapy or targeted therapy to assess response — often weeks before CT scans show changes
- Minimal residual disease (MRD): Detecting microscopic disease after curative surgery — predicting relapse risk
- Resistance mutations: Identifying new mutations when a targeted therapy stops working, without repeat tumour biopsy
- Multi-cancer early detection: Annual screening in high-risk individuals (age 50+, family history, smoking history)
Liquid Biopsy vs. Standard Tissue Biopsy
| Feature | Liquid Biopsy | Tissue Biopsy |
|---|---|---|
| Invasiveness | Blood draw only | Surgical procedure |
| Turnaround | 5-7 days | 7-14 days |
| Tumour heterogeneity | Captures whole-body signal | Single site only |
| Sensitivity (early stage) | Lower (20-40%) | High (gold standard) |
Availability in Istanbul
Foundation One Liquid CDx, FoundationOne CDx (tissue), and the GRAIL Galleri multi-cancer early detection test are available at accredited Istanbul oncology centres. Comprehensive liquid biopsy panels analysing EGFR, KRAS, BRAF, PIK3CA, ESR1, HER2 and over 70 additional clinically relevant genes cost $1,500–$4,000 in Istanbul — compared to $5,000–$8,000 in the USA.
Corcoran RB & Chabner BA (2018) NEJM; Oxnard et al. PATHFINDER (2023) Cancer Discovery; FDA Foundation One Liquid CDx Label 2022; NCCN Biomarker Guidelines 2026.
Find out if a liquid biopsy test is appropriate for your situation.
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