# Circulating tumour cell clearance as the phase 2 gate for anti-metastatic drugs

Source: https://onco.cc/ideas/idea-bio2-ctc-clearance-go-nogo/  
OnCo record `idea-bio2-ctc-clearance-go-nogo` (Idea). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

Cancer cells travelling in the blood can be counted. If a drug clears them, that is an early sign it may stop spread, and it reads out in weeks rather than years.

## Summary

CTC count is an established prognostic marker in metastatic breast, prostate and colorectal cancer, and CTC conversion from unfavourable to favourable has been used as a response measure in prostate cancer. Anti-metastatic mechanisms such as platelet cloaking, trap-mediated capture and cluster formation should show up as CTC and CTC-cluster clearance long before imaging changes. A standardised cluster readout would give small, cheap, fast phase 2 decisions.

## Fields

- Kind: Idea
- Last checked: 2026-09-08
- Hypothesis: Failure to reduce CTC cluster burden by half at four weeks predicts absence of metastasis-free survival benefit with high negative predictive value, allowing most anti-metastatic candidates to be killed in trials of under 60 patients.
- Rationale: Clusters rather than single cells carry most metastatic potential in mouse and human studies, and their abundance is dynamic and drug-responsive. Clearance-based go/no-go decisions already work in leukaemia through MRD and in prostate cancer through PSA and CTC conversion.
- Proposed test: Add a harmonised CTC and cluster assay to three ongoing perioperative or adjuvant trials, and test the association between four-week clearance and relapse; publish the assay and thresholds openly.
- Maturity: early-clinical
- Actor: industry

## Sources

- Bottleneck evidence (Metastasis is understood least and studied last): Dillekås et al., Are 90% of deaths from cancer caused by metastases? (Cancer Medicine 2019): https://doi.org/10.1002/cam4.2474

## Connected records

- cancers: [HR-positive / HER2-negative breast cancer](https://onco.cc/cancers/breast-hr-positive/), [Prostate cancer](https://onco.cc/cancers/prostate/)
- technologies: [Liquid biopsy (ctDNA)](https://onco.cc/technologies/liquid-biopsy/), [MRD / molecular residual disease testing](https://onco.cc/technologies/mrd-testing/)
- terms: [Circulating tumour DNA (ctDNA)](https://onco.cc/terms/ctdna/), [Minimal / molecular residual disease (MRD)](https://onco.cc/terms/mrd/)
- people: [Caroline Dive](https://onco.cc/people/caroline-dive/), [Klaus Pantel](https://onco.cc/people/klaus-pantel/)
- bottlenecks: [Biomarkers are not validated or standardised](https://onco.cc/bottlenecks/b-biomarker-validation/), [Metastasis is understood least and studied last](https://onco.cc/bottlenecks/b-metastasis-biology/)
- key papers: [Are 90% of deaths from cancer caused by metastases?](https://onco.cc/key-papers/paper-dillekas-cancer-med/)

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