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Reducing abemaciclib, palbociclib and ribociclib after complete response in HER2‑negative metastatic breast cancer

Verified siteRegistered drugNo placebo
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What is this trial about?

A plain-language summary of the goals, design and what participants do

The study focuses on people with HER2-negative metastatic breast cancer, a type of breast cancer that has spread beyond the breast and does not have the HER2 protein. Standard treatment for this condition often includes hormone therapy called an aromatase inhibitor together with a class of medicines known as CDK4/6 inhibitors. In this trial the specific drugs used are abemaciclib, palbociclib and ribociclib, all taken by mouth. The main goal is to find out whether lowering or stopping the CDK4/6 inhibitor after a patient has had a complete or partial response (meaning the cancer has shrunk a lot or disappeared on scans) and a negative test for circulating tumor DNA (ctDNA) is not worse than continuing the full treatment, as measured by Progression-Free Survival (the time a person lives without the cancer getting worse).

Participants who have already been on the combined therapy for at least two years and meet the response criteria will be randomly assigned to either keep taking the CDK4/6 inhibitor or stop it while continuing the aromatase inhibitor. Over the following months, they will have regular doctor visits, imaging scans evaluated using the RECIST 1.1 criteria (a way doctors judge if cancer has grown), and blood tests that may include the Signatera™ test to look for ctDNA. They will also complete quality‑of‑life questionnaires such as the EuroQol EQ-5D-5L at set intervals. The study will follow each person for several years to see how long they stay free of cancer progression and to monitor any side effects.

The research process

The trial runs in 6 steps – from screening to follow-up. Each step says what happens and what the team monitors.

  1. Step 1

    Baseline Visit and Randomization

    After enrollment you attend a baseline visit where medical imaging and a blood test for circulating tumor DNA (ctDNA) are performed.

    You complete the EuroQol EQ-5D-5L and EORTC‑QLQ‑C30 questionnaires that record your health status.

    Based on the study design you are randomly assigned to either continue the full dose of a CDK4/6 inhibitor or to receive a reduced dose.

  2. Step 2

    Start of Assigned Medication

    If you are assigned to the full‑dose arm you take the study drug at the standard strength:

    Abemaciclib 300 mg taken orally once daily, or

    Palbociclib 125 mg taken orally once daily, or

    Ribociclib 600 mg taken orally once daily.

    If you are assigned to the reduced‑dose arm the same medicines are given at a lower strength, as defined by the study protocol.

    The medication is taken every day for as long as you remain in the trial, unless disease progression or unacceptable side effects occur.

  3. Step 3

    Regular Follow‑Up Visits (First Two Years)

    Every three months you return for a follow‑up visit.

    During each visit you undergo clinical evaluation, imaging studies to check for disease progression, and a blood draw for ctDNA testing.

    You also complete the EuroQol EQ-5D-5L and EORTC‑QLQ‑C30 questionnaires again.

    Any side effects are recorded and graded according to standard safety criteria.

  4. Step 4

    Extended Follow‑Up Visits (After Two Years)

    After the first two years, follow‑up visits occur every six months.

    The same assessments are performed: clinical check, imaging, ctDNA test, and patient‑reported outcome questionnaires.

    Safety monitoring continues at each visit.

  5. Step 5

    Safety Monitoring Throughout the Trial

    At every visit you are asked about any new symptoms or side effects.

    Laboratory tests may be taken to evaluate organ function.

    Serious adverse events are reported immediately to the study team.

  6. Step 6

    End of Study

    The trial ends for you when disease progression is documented, you discontinue the study medication, you experience an adverse event that requires stopping treatment, or the overall study reaches its planned completion date.

    Final assessments, including imaging and ctDNA analysis, are performed at the end of the study.

Who can join the trial?

12 criteria

  • You must sign a written consent form before any study procedures (or have an impartial witness sign for you if you cannot sign yourself).
  • You need to be part of a social security system.
  • You must be willing and able to follow the study plan, including taking the medication, attending scheduled visits, undergoing examinations, and completing follow‑up.
  • You must be 18 years of age or older, and you can be either female or male.
  • You must have a diagnosed breast adenocarcinoma that has come back locally or spread (metastatic) and cannot be treated with local therapy, and the tumor must be hormone‑receptor positive (meaning at least 10 % of the cancer cells show estrogen or progesterone receptors when tested).
  • Your tumor must be HER2‑negative as defined by standard lab tests: an immunohistochemistry (IHC) score of 0 or 1+, or a score of 2+ with a negative in‑situ hybridization (ISH) result (HER2/CEP17 ratio < 2 or HER2 copy number < 4).
  • You must have had a complete response, or a partial response that involves only hard (sclerotic) bone disease, and this response must have lasted for at least 6 months, measured by the RECIST 1.1 criteria on CT scans.
  • You need to have an archived tumor tissue sample that can be used for next‑generation sequencing (NGS) to create a personalized circulating tumor DNA (ctDNA) test.
  • You must be receiving first‑line metastatic treatment with a CDK4/6 inhibitor combined with an aromatase inhibitor (with or without a luteinizing‑hormone‑releasing hormone (LHRH) agonist) for at least 24 months.
  • Your overall health must be good enough to have an ECOG performance status of 0 or 1 (fully active or restricted in physically strenuous activity but ambulatory).
  • If you are a woman who could become pregnant, you must have a negative pregnancy test within 28 days before starting the study and use a highly effective non‑hormonal birth control method during the study and for at least 3 weeks after the last dose.
  • If you are a man who may have sexual contact with a woman who could become pregnant, you must be surgically sterile or use an acceptable form of birth control until at least 3 weeks after the last dose (or 14 weeks if you are taking the drug palbociclib).

Who cannot join the trial?

11 criteria

  • Detectable tumor‑derived ctDNA at screening: This means tiny pieces of cancer DNA can be found in your blood using a test called the Signatera™ Genome test.
  • Legal guardianship, imprisonment, or inability to give informed consent: If you are under a legal guardian, placed in jail, or cannot understand and agree to the study, you cannot take part.
  • Unwilling or unable to follow required medical follow‑up: If you cannot attend scheduled visits because of distance, social circumstances, or mental health reasons, you are excluded.
  • Disease progression while on a CDK4/6 inhibitor: If your cancer gets worse while taking a CDK4/6 inhibitor (a medicine that blocks proteins helping cancer grow), you cannot join.
  • Prior chemotherapy for advanced or metastatic disease: Having received cancer‑killing drugs for advanced cancer before makes you ineligible.
  • Major surgery within the past 2 weeks: If you had a large operation less than two weeks ago, you cannot participate.
  • History of another malignancy: Having had any other cancer besides the breast cancer being studied, except for well‑treated skin cancers (basal cell or squamous cell carcinoma) or early‑stage cervical cancer, and only if you have been cancer‑free and off treatment for at least 3 years.
  • Carcinomatous meningitis or central nervous system metastases: This refers to cancer that has spread to the lining of the brain/spinal cord or to the brain itself.
  • Pregnant, breastfeeding, or unwilling to use highly effective contraception: Women who are pregnant, nursing, or not willing to use strong birth control cannot join.
  • Any medical condition that could interfere with study procedures or compliance: Any other health problem that might make it hard to follow the study plan excludes you.
  • Current participation in another interventional clinical trial or recent use of an investigational agent: Being in another drug study or having taken a new experimental medication within 28 days before enrollment (or during the study) disqualifies you.
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Investigated drugs

  • Verzenios

    is a pill taken by mouth that contains the medicine abemaciclib. In this study, it is one of the drugs that blocks proteins called CDK4 and CDK6, which help cancer cells grow. Patients first took Verzenios together with another hormone‑blocking drug (an aromatase inhibitor) for at least two years. The trial then looked at whether reducing or stopping Verzenios still kept the cancer from getting worse.

  • IBRANCE

    is a capsule (or tablet) taken by mouth that contains the medicine palbociclib. Like Verzenios, it works by stopping CDK4 and CDK6 proteins, slowing down the growth of breast cancer cells that need estrogen. In the trial, patients used IBRANCE with an aromatase inhibitor for a long period, and the researchers tested if lowering the dose or stopping it would still protect patients from cancer progression.

  • Kisqali

    is a film‑coated tablet taken by mouth that contains the medicine ribociclib. It also blocks CDK4 and CDK6, helping to keep estrogen‑driven breast cancer from growing. The study gave Kisqali together with an aromatase inhibitor for at least two years, then examined whether a reduced amount or stopping the drug would still be safe and effective for patients who had responded well.

What is already known about the treatment

  • Verzenios 150 mg film-coated tablets

    This medication is taken by mouth as a film‑coated tablet that is swallowed whole. It is an approved drug used for treating certain advanced breast cancers that are HER2‑negative. It works by blocking proteins called CDK4 and CDK6, which helps stop cancer cells from dividing. It belongs to the class of CDK4/6 inhibitor anticancer medicines.

  • IBRANCE 125 mg hard capsules

    This drug is taken orally as a hard capsule that is swallowed with water. It is an approved treatment for HER2‑negative metastatic breast cancer in patients whose tumors have hormone receptors. The capsule contains palbociclib, which blocks CDK4 and CDK6 enzymes, slowing down the growth of cancer cells. It is classified as a CDK4/6 inhibitor used in oncology.

  • Kisqali 200 mg film-coated tablets

    This medication is taken by mouth as a film‑coated tablet that is swallowed whole. It is approved for use in HER2‑negative advanced breast cancer that responds to hormone therapy. Ribociclib, the active ingredient, blocks the CDK4/6 proteins, reducing the ability of cancer cells to multiply. It falls under the CDK4/6 inhibitor class of anticancer drugs.

Investigated diseases

HER2-negative metastatic or locoregional breast cancer - It is a breast cancer that does not overexpress the HER2 protein, meaning it is classified as HER2‑negative. The disease can be confined to the breast and nearby lymph nodes (locoregional) or have spread to distant organs (metastatic). Cancer cells grow and divide, forming tumors that may increase in size and number over time. In the metastatic setting, tumor cells travel through the bloodstream or lymphatic system to other parts of the body, such as bone, liver, lung, or brain. As the disease progresses, new lesions can appear and existing lesions can become larger, which can be detected by imaging or molecular tests. The condition typically follows a pattern of gradual growth unless intervened upon.
Trial detailsLast updated 6 Nov 2026
Age18+ yearsPhasePhase IIITrial ID2026-526319-12-00Protocol codeUC-BCG-2525Estimated enrolment802 patientsSponsorUnicancer

sourced from the EU Clinical Trials Register and site verification

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