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Study on the Safety and Effectiveness of Vepdegestrant and Samuraciclib for Adults with ER+ Advanced or Metastatic Breast Cancer

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What is this trial about?

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

This clinical trial is focused on studying treatments for Advanced or Metastatic Breast Cancer, specifically in patients whose cancer is ER-positive and HER2-negative. The study will explore the effects of a new treatment combination involving two medications: Vepdegestrant (ARV-471) and Samuraciclib. Vepdegestrant is a type of medicine known as a proteolysis targeting chimera, which is designed to help the body break down certain proteins that may be involved in cancer growth.

The purpose of the study is to investigate the safety and effectiveness of this combination treatment. Participants will receive the medications orally, with Vepdegestrant provided as a capsule and Samuraciclib as a film-coated tablet. The study will be conducted in two phases. The first phase will focus on assessing how well participants tolerate the treatment and determining the best dose to use. The second phase will evaluate the treatment's ability to reduce or control the cancer.

Throughout the study, participants will be monitored for any side effects and changes in their cancer. The study will also look at how the two medications interact with each other in the body. This research aims to provide valuable information on whether this combination of treatments can be a safe and effective option for people with this type of breast cancer.

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

    Joining the study

    Upon joining the study, eligibility is confirmed based on specific criteria, including age and diagnosis of advanced or metastatic breast cancer.

    A tumor sample is required for inclusion, either from a recent biopsy or archival tissue.

  2. Step 2

    Initial assessment

    An initial assessment is conducted to evaluate the current health status and establish a baseline for the study.

    This includes measuring any lesions as defined by specific guidelines.

  3. Step 3

    Phase 1b: Safety and tolerability assessment

    The first phase focuses on assessing the safety and tolerability of the combination of ARV-471 and samuraciclib.

    Participants receive the medications orally in the form of capsules and film-coated tablets.

    The dosage and frequency are determined by the study protocol, and the observation period includes monitoring for any dose-limiting side effects.

  4. Step 4

    Phase 2: Antitumor activity assessment

    The second phase evaluates the antitumor activity of the medication combination.

    Participants continue to receive the medications as prescribed, with regular assessments to monitor tumor response.

    The effectiveness is measured by the reduction in tumor size or other clinical indicators.

  5. Step 5

    Regular monitoring and assessments

    Throughout the study, regular monitoring is conducted to track any side effects and the overall health status.

    This includes laboratory tests, ECGs, and other necessary evaluations to ensure safety.

  6. Step 6

    Completion of the study

    The study is estimated to conclude by June 2027.

    Final assessments are conducted to evaluate the long-term effects and overall outcomes of the treatment.

Who can join the trial?

11 criteria

  • Participants must be **18 years or older** at the time of screening.
  • Must have a **diagnosis of breast cancer** that cannot be removed by surgery to cure it. This includes having at least **1% of cells with ER+** (estrogen receptor positive) and **HER2-** (human epidermal growth factor receptor 2 negative) as determined by the most recent tumor biopsy.
  • Participants with **breast cancer in both breasts** that are both ER+/HER2- are eligible.
  • A **tumor sample** collected at the time of diagnosis with local recurrent or metastatic disease or an **archival tumor tissue** is required for inclusion.
  • For prior cancer treatments:
    • Up to **2 previous treatments** for advanced or metastatic disease are allowed.
    • Only **1 previous chemotherapy** is allowed, and it must not include antibody-drug conjugates.
    • Up to **2 previous hormone-based treatments** are allowed.
    • No previous experimental hormone therapy or a drug called **elacestrant** is allowed.
    • Must have had **1 previous treatment** with a CDK4/6 inhibitor-based regimen.
    • Participants must have at least **1 measurable tumor** as defined by specific criteria (RECIST v1.1). If the cancer is only in the bones, at least one bone lesion must have a measurable part.
    • Participants must have an **ECOG performance status** of 0 or 1, which means they are fully active or have some symptoms but can still do light work. There should be no worsening of this status in the last 2 weeks.

Who cannot join the trial?

4 criteria

  • Participants with other types of cancer that are not **advanced or metastatic breast cancer** cannot join the study. **Advanced or metastatic breast cancer** means the cancer has spread beyond the breast to other parts of the body.
  • Participants who are not within the specified age range for the study cannot participate. The study is open to adults, which typically means individuals 18 years and older.
  • Participants who are not female or male cannot join the study. The study is open to both genders.
  • Participants who are part of a vulnerable population, such as those unable to give consent or those with certain disabilities, are not eligible for the study.
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Investigated drugs

  • Vepdegestrant (ARV-471/PF-07850327)

    is an oral medication being studied for its ability to target and break down specific proteins in cancer cells. It is being tested to see if it can help treat advanced or metastatic breast cancer that is positive for estrogen receptors (ER+). This medication is part of a new class of treatments known as proteolysis targeting chimeras, which aim to remove harmful proteins from the body.

  • Samuraciclib

    is another medication being tested in combination with Vepdegestrant. It is being studied for its potential to enhance the effects of Vepdegestrant in treating ER+ advanced or metastatic breast cancer. Researchers are examining how these two medications work together to improve treatment outcomes for patients.

What is already known about the treatment

  • Vepdegestrant

    This medication is administered orally and is currently being studied in clinical trials for its safety and effectiveness in treating advanced or metastatic breast cancer. It is a proteolysis targeting chimera, which means it works by marking specific proteins for degradation, thereby reducing their levels in the body. This mechanism helps in controlling the growth of cancer cells. Vepdegestrant is classified as an anticancer agent and is being evaluated for its potential to improve outcomes in patients with estrogen receptor-positive breast cancer.

  • Samuraciclib

    This medication is also taken orally and is under investigation in clinical trials for its role in treating advanced or metastatic breast cancer. It functions by inhibiting certain enzymes that are crucial for cancer cell division and growth. As a cyclin-dependent kinase inhibitor, samuraciclib aims to slow down or stop the progression of cancer. It is being studied in combination with other treatments to assess its effectiveness and safety in improving cancer treatment outcomes.

Investigated diseases

Advanced or Metastatic Breast Cancer – This is a stage of breast cancer where the disease has spread beyond the breast and nearby lymph nodes to other parts of the body. It often affects organs such as the bones, liver, lungs, or brain. The progression of the disease can vary, with some individuals experiencing rapid spread while others may have a slower progression. Symptoms can include pain, fatigue, and other signs depending on the organs affected. The disease is typically characterized by its resistance to standard treatments, requiring more targeted therapeutic approaches. It is often monitored through imaging and other tests to assess the extent of spread and response to treatment.
Trial detailsLast updated 2 Oct 2026
Age18+ yearsPhasePhase ITrial ID2023-507125-41-00Protocol codeC4891024Estimated enrolment67 patientsSponsorPfizer Inc.

sourced from the EU Clinical Trials Register and site verification

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© 2026 Clinical Trials EU – European Clinical Trials Information Network

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On this site, “treatment” means an investigational medicine being studied in a clinical trial. Its safety and efficacy for the use being studied have not yet been confirmed, some participants may receive a placebo or a comparator medicine, and taking part does not guarantee any health benefit. The decision to take part is made by the doctor at the research site. This site is for information only and does not replace medical advice.

This service is not affiliated with the European Commission, the EMA, or the official CTIS system. Most information comes from publicly available international clinical-trial registries, supplemented by data from academic sites, national regulators and commercial sponsors. On this site, “treatment” and “therapy” mean a medicine being tested in a clinical trial. Its safety and effectiveness in the use being studied are not yet confirmed, some participants may receive a placebo or a comparator, and taking part does not guarantee a health benefit. The doctor at the research site decides who can take part. This site provides information, not medical advice. Certain content and visual elements on this website have been generated or enhanced using artificial intelligence (AI).