Circulating Tumour Cell (CTC) Count
CTC Count
Circulating Tumour Cell (CTC) testing isolates and counts rare cancer cells that have shed from a primary or metastatic tumour and entered the bloodstream. Unlike ctDNA (which detects DNA fragments), CTC tests capture intact cancer cells — enabling not only counting but also molecular characterisation, culture, and drug sensitivity testing (as in the RGCC platform). CTC count is an established prognostic marker: higher counts correlate with poorer outcomes in breast, prostate, and colorectal cancers.
What It Measures
- Total CTC count per 7.5 ml blood (CELLSEARCH validated threshold: ≥5 CTCs = poor prognosis in metastatic breast cancer)
- CTC morphology and cell characterisation
- Expression of EpCAM (epithelial marker), cytokeratins 8/18/19
- In extended panels: HER2, androgen receptor, PD-L1, EMT markers on CTCs
- In RGCC platform: live CTC drug sensitivity testing
- Cancer stem cell markers (CD44, CD24, ALDH1) in research panels
How It Works
Blood (7.5 ml for CELLSEARCH; 8–10 ml for RGCC) is collected in a special CellSave tube. For CELLSEARCH (the only FDA-cleared CTC platform), an automated immunomagnetic capture system selects EpCAM-positive cells, labels them with fluorescent antibodies against cytokeratins, and counts them using an automated digital imaging system. For research/functional platforms (RGCC, ISOFLUX), additional steps culture the isolated CTCs for functional testing.
Who Should Consider This Test
- Metastatic breast, prostate, or colorectal cancer patients for prognosis monitoring
- Patients mid-treatment to assess whether CTCs are decreasing (treatment response)
- Those with rising tumour markers where imaging has not yet confirmed progression
- Patients using RGCC-type testing for integrative oncology chemosensitivity guidance
- Clinical trial participants requiring baseline and serial CTC measurements
Evidence Summary
CTC count is FDA-cleared (CELLSEARCH) as a prognostic aid in metastatic breast, prostate, and colorectal cancers. Multiple large studies confirm that CTC ≥5/7.5 ml at baseline in metastatic breast cancer predicts significantly shorter PFS and OS (SWOG S0500 trial). In prostate cancer, CTC count outperforms PSA as a surrogate for overall survival in multiple trials. However, CTC count has not been prospectively validated as a treatment-selection tool — it tells you prognosis but does not independently guide which therapy to choose. CTC functional testing (RGCC) remains in the preliminary evidence category for clinical utility.
Available Labs & Providers
This list is not exhaustive. Ask your oncologist or integrative physician for locally available options.
Important Considerations
- Low CTC shedding in early-stage or localised cancers — test most useful in metastatic setting
- CTC count fluctuates — single measurements are less informative than serial monitoring
- EpCAM-based capture misses CTCs that have undergone epithelial-to-mesenchymal transition (the most aggressive subpopulation)
- A low or undetectable CTC count does not mean no cancer activity — false negatives occur
- CTC count should complement, not replace, imaging and clinical assessment
Related Tests
Informational only. Not medical advice. Always consult your oncologist before ordering or acting on any diagnostic test.