# Take the blood test, and give the drug, at the right time of day

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

## TL;DR

Cancer cells enter the blood mostly during rest, so a morning blood test may miss them. Sampling and dosing at the right hour may be a free improvement.

## Summary

Circulating tumour cell shedding in breast cancer patients and mouse models peaks during the rest phase, with several-fold differences between night and day samples. Almost all clinical sampling occurs in clinic hours, and almost all therapy is delivered in clinic hours. If shedding and proliferation are circadian, both assay sensitivity and drug timing are currently set by convenience.

## Fields

- Kind: Idea
- Last checked: 2026-09-08
- Hypothesis: Plasma ctDNA and CTC yield are at least twofold higher in samples taken during the rest phase, raising MRD assay sensitivity without any change in chemistry; and rest-phase dosing of a cycle-dependent agent increases kill of shed cells.
- Rationale: Chronotherapy has reproducible pharmacokinetic effects and a randomised precedent in colorectal chemotherapy timing. Sampling time is the cheapest variable in the whole MRD pipeline and has never been optimised.
- Proposed test: A crossover sampling study of 60 patients with paired rest-phase and active-phase draws analysed by the same assay; if yield differs, change guidance and then test timed dosing.
- Maturity: preclinical-evidence
- Actor: research

## Sources

- Bottleneck evidence (Dormant cells and minimal residual disease): Tie et al., ctDNA analysis guiding adjuvant therapy in stage II colon cancer (NEJM 2022): https://doi.org/10.1056/NEJMoa2200075

## Connected records

- cancers: [HR-positive / HER2-negative breast cancer](https://onco.cc/cancers/breast-hr-positive/)
- 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: [Klaus Pantel](https://onco.cc/people/klaus-pantel/)
- bottlenecks: [Biomarkers are not validated or standardised](https://onco.cc/bottlenecks/b-biomarker-validation/), [Dormant cells and minimal residual disease](https://onco.cc/bottlenecks/b-dormancy-mrd/)

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