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Blood tests could reveal hidden resistance in breast cancer

NCT ID NCT07701070

Knowledge-focused Sponsor: AstraZeneca Source: ClinicalTrials.gov ↗

What the study statuses mean

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Recruitment status, easiest to join first

Recruiting now
This trial is taking on new participants right now.
Not yet recruiting This study
Registered, but not yet taking participants.
By invitation only
Not open to general applications. Only people the study team invites can take part.
Paused
Paused for now. It may or may not start again.
Ongoing
Running, but no longer taking on new participants.
Completed
The trial has finished. Results may not be published yet.
Stopped early
Stopped early, before it reached the end. That can be for many reasons, including safety.
Cancelled
Cancelled before anyone took part.

Expanded access (not trials)

Expanded access
Not a trial. This treatment can be requested outside a study, case by case, for people who qualify.
Expanded access (paused)
Not a trial. The treatment can normally be requested outside a study, but is unavailable right now.
Expanded access (ended)
Not a trial. The treatment could once be requested outside a study, but no longer can.
Approved
The treatment has been approved, so it is available normally rather than through this programme.

When the status isn't known

Details not published
The full record has not been published yet, so there is little to show here.
Status unknown
This status has not been confirmed recently, so it may be out of date.

First seen Jul 14, 2026 · Last updated Jul 15, 2026 · Updated 1 time

Summary

This study observes people with a common type of advanced breast cancer (HR+/HER2-) who are already on standard hormone therapy. Researchers use simple blood tests to look for changes in the ESR1 gene, which can make the cancer stop responding to treatment. By tracking these mutations over time, the study aims to better understand how resistance develops and when it might appear.

What this could mean

Our plain-language read of the trial. This is informational only, not medical advice or a prediction.

What this could lead to
If successful, this study could help doctors predict when breast cancer might become resistant to hormone therapy, potentially guiding earlier treatment changes.
What could go wrong
This is an observational study, not a treatment trial, so it does not test a new therapy. The findings may not directly improve patient outcomes.

This is an AI summary of the original study and may miss details. Read our disclaimer.

Study facts

What this study's own registry entry says, in plain language.

Participants

About 3,000 people

The number the study aims to enrol. It can still change while the study runs.

Expected to start

Sep 2026

An estimate. Start dates often move.

Expected to finish

Mar 2029

An estimate. End dates often move.

Lead sponsor

A company

The lead sponsor is a pharmaceutical, biotech, or medical-device company.

Who can take part

This study's own entry requirements. Only the study team can say for certain whether you qualify.

Who is studied

Adults with HR-positive/HER2-negative advanced breast cancer (aBC), receiving first-line aromatase inhibitor (AI) plus CDK4/6 inhibitor therapy for 6-18 months, without disease progression, and with unknown ESR1 status at baseline.

Ages

18 to 130 years

Sex

Anyone

Healthy volunteers

Not accepted

This study is not open to healthy volunteers. The entry requirements below say who it is open to.

Show the full entry requirements

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: * Age 18 years or older at the time of informed consent and willing and able to provide informed consent before any study-related procedures. * Histologically- or cytologically-confirmed hormone receptor-positive (ER- and/or progesterone receptor-positive), human epidermal growth factor receptor 2-negative (HER2-negative) advanced breast cancer. * Receiving first-line therapy with an aromatase inhibitor in combination with a CDK4/6 inhibitor for at least 6 months and no more than 18 months, with no evidence of disease progression at study entry, as assessed by the investigator. * Able and willing to provide a blood sample for circulating tumour DNA testing for ESR1 mutation assessment at approximately quarterly intervals. Exclusion Criteria: * Evidence of disease progression during first-line aromatase inhibitor plus CDK4/6 inhibitor therapy, based on investigator assessment. * Known ESR1 mutation status at study entry.

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Conditions

The condition(s) this trial relates to.

breast cancer hormone receptor-positive breast cancer

As listed by the trial registrant

The condition terms exactly as the trial's registrant entered them.

Advanced breast cancer

How to take part

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  1. The official record

    ClinicalTrials.gov lists the study team's own contact details, including names and phone numbers. We don't republish those.

    Open the record ↗

  2. A doctor treating you

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