Therapy & companion diagnostics ↗
Extends the existing companion-diagnostic question for the same drug and test with European certification and additional trial evidence.
Frozen card revision. This is the recorded reading, not an automatically refreshed view. Current card ↗
Commercialization · TOPIC v1
Changing treatment before scans show progression: a new relationship between breast cancer drugs and blood tests
What benefit comes from detecting a resistance mutation and switching treatment before radiographic progression?
2026-10-13 13:52:46.719 UTC · Last recorded update
CURRENT READING
European certification was added for Guardant360 CDx. Earlier switching prolonged PFS in selected SERENA-6 patients, while SERENA-4 under different conditions missed its primary endpoint. FDA requires confirmation comparing early switching with switching at progression.
Recorded editorial state, not a maturity score
- PFS benefit in selected patientsRecorded
- Compare early and progression-time switchingUnverified
- Long-term benefit and uptakeUnverified
New question opened · v1
Linked European CDx certification, SERENA-6, SERENA-4 and FDA confirmation requirements through the question of treatment timing.
Permanent link to this revision ↗01 / WHAT WE TRACK
What benefit comes from detecting a resistance mutation and switching treatment before radiographic progression?
02 / EVIDENCE & TECHNOLOGY
ctDNA / ESR1 mutations / Guardant360 CDx / camizestrant / CDK4/6 inhibitors
03 / EDITORIAL READING
A test can guide when to use a drug as well as which drug to use. The value of repeated monitoring depends on the benefit of acting on its results.
04 / WHAT REMAINS UNKNOWN
This concerns advanced breast cancer during treatment, not early cancer screening. Differences between trials cannot be attributed to patient selection alone; PFS is not overall survival. Repeat-test uptake, revenue and cost-effectiveness remain unverified.
05 / NEXT CHECK
Comparison of early and post-progression use of the same drug, longer-term survival and uptake in the indicated population.
A hypothesis to keep honest
HYPOTHESIS · NOT YET TESTEDA test that demonstrates benefit in treatment timing may expand from one-off drug selection to ongoing treatment decisions.
What would change our view: Reconsider if early switching offers no advantage over later switching, or the burdens of repeated testing and earlier treatment outweigh the benefit.
A prospective test proposal, not a prediction score. A graph connection does not validate this hypothesis.
Linked people & organizations
Open an entity to find its cardsCOMPANYGuardant Health ↗
Provider of Shield and Guardant360 CDx; distinct products and uses.
Evidence: Guardant Health ↗FDA ↗
INSTITUTION / INFRASTRUCTUREGuardant360 CDx ↗
Mentioned in this issue
INSTITUTION / INFRASTRUCTURECamizestrant / Etcamah ↗
Mentioned in this issue
Related questions, optional follows
Map ↗Signatera: Using Tumor DNA in Blood to Guide Treatment After Surgery ↗
Compares postoperative treatment selection with timing a switch during treatment, across different cancers and products rather than comparing test performance.
Latest card updates
Latest 5 · editorial record dates- v1 · 2026-10-13 13:52:46.719 UTCNew question opened
Linked European CDx certification, SERENA-6, SERENA-4 and FDA confirmation requirements through the question of treatment timing.
Reading at the time: European certification was added for Guardant360 CDx. Earlier switching prolonged PFS in selected SERENA-6 patients, while SERENA-4 under different conditions missed its primary endpoint. FDA requires confirmation comparing early switching with switching at progression.
Earlier updates (0)
Earlier entries will appear here once more than five reader-facing revisions have accumulated.
Background readings
Source dates and verification scope
Guardant360 CDx: European IVDR certification for camizestrant treatment selection ↗
Guardant Health · 2026-10-08 · company-announcement
SERENA-6: camizestrant after detection of an ESR1 mutation ↗
New England Journal of Medicine / PubMed · 2025-06-01 · peer-reviewed-study
Camizestrant accelerated approval letter and confirmatory requirements ↗
US Food and Drug Administration · 2026-09-04 · regulatory-document
SERENA-6 updated progression results ↗
AstraZeneca · 2026-06-02 · company-announcement
Update on the SERENA-4 Phase III trial ↗
AstraZeneca · 2026-09-11 · company-announcement
Etcamah: European public assessment information ↗
European Medicines Agency · · regulatory-information