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Study Comparing ARV-471 and Fulvestrant for Patients with Advanced Estrogen Receptor-Positive, HER2-Negative Breast Cancer After Endocrine Treatment

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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 Breast Cancer, specifically in patients with Estrogen Receptor-Positive (ER+) and HER2-Negative (HER2-) types. The study compares two treatments: a new drug called ARV-471 (PF-07850327), which is taken as a film-coated tablet, and an existing medication called Fulvestrant, which is given as an injection. The purpose of the study is to see if ARV-471 is better than Fulvestrant in helping patients live longer without their cancer getting worse.

Participants in the study will be randomly assigned to receive either ARV-471 or Fulvestrant. The study will last for up to 36 months, during which time participants will have regular check-ups and tests to monitor their health and the progress of their cancer. The study will also include a group of participants who will receive a placebo, which is a substance with no active medication, to help compare the effects of the treatments.

The trial aims to provide valuable information on the effectiveness and safety of ARV-471 compared to Fulvestrant for patients with this type of breast cancer. This research could lead to improved treatment options for those whose disease has progressed after previous hormone-based therapies. Participants will be closely monitored by healthcare professionals throughout the study to ensure their safety and well-being.

The research process

The trial runs in 5 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, you will be randomly assigned to one of two groups. One group will receive the medication ARV-471 in the form of a film-coated tablet taken orally. The other group will receive Fulvestrant as a solution for injection administered intramuscularly.

    The purpose of this study is to compare the effectiveness of ARV-471 with Fulvestrant in treating advanced breast cancer that is estrogen receptor-positive and HER2-negative.

  2. Step 2

    Medication administration

    If you are in the ARV-471 group, you will take the medication orally as prescribed by the study team. The dosage and frequency will be explained to you during your visits.

    If you are in the Fulvestrant group, you will receive the medication through an intramuscular injection. The study team will administer these injections at scheduled intervals.

  3. Step 3

    Regular visits

    You will be required to attend regular visits to the study center. During these visits, the study team will monitor your health and the progress of your treatment.

    These visits will include physical examinations, blood tests, and other necessary assessments to ensure your safety and to evaluate the effectiveness of the treatment.

  4. Step 4

    Monitoring and assessments

    Throughout the study, your health will be closely monitored. This includes regular assessments of your cancer's response to the treatment.

    The study team will use imaging tests and other diagnostic tools to track any changes in your condition.

  5. Step 5

    Completion of the study

    The study is expected to continue until May 2028. You will be informed about the duration of your participation and any follow-up procedures required after the study ends.

    Upon completion, the study team will discuss the results with you and provide information on any further treatment options if necessary.

Who can join the trial?

12 criteria

  • Participants must be aged 18 years or older.
  • Female participants under 60 years old who have stopped having regular periods for 12 months must have a hormone level test to confirm menopause.
  • Pre-menopausal and peri-menopausal women, as well as men, must agree to use a medication called an LHRH agonist, which helps control hormone levels.
  • Women of childbearing potential and men must agree to use contraception to prevent pregnancy during the study.
  • Participants must be willing and able to attend all scheduled visits, follow the treatment plan, and complete all tests and procedures required by the study.
  • Participants must have a confirmed diagnosis of breast cancer that has returned or spread to other parts of the body and cannot be treated with surgery or radiation to cure it.
  • The cancer must be ER(+), meaning it has estrogen receptors, and HER2(-), meaning it does not have too many HER2 proteins. This must be confirmed by a test on the most recent tumor sample.
  • Participants must provide a blood sample and a tumor sample from the time the cancer returned or spread. If not available, a new biopsy is required.
  • Participants must have had one previous treatment with a CDK4/6 inhibitor combined with hormone therapy, and no more than one additional hormone therapy.
  • The most recent hormone treatment must have been given for at least 6 months before the cancer progressed.
  • Participants must have at least one measurable tumor, or if they have only bone disease, they must have non-measurable disease.
  • Participants must have an ECOG performance status of 0 or 1, which means they are fully active or have some symptoms but can still carry out light work.

Who cannot join the trial?

4 criteria

  • Patients who have not received prior treatment for their advanced breast cancer.
  • Patients with breast cancer that is not ER(+) or HER2(-). ER(+) means the cancer grows in response to the hormone estrogen. HER2(-) means the cancer does not have high levels of the protein HER2.
  • Patients who are not within the specified age range for the study.
  • Patients who are part of a vulnerable population, which means they might need special protection or care.
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Investigated drugs

  • ARV-471

    is an experimental medication being tested to see if it can help people with a specific type of breast cancer. This type of breast cancer is called estrogen receptor-positive, HER2-negative advanced breast cancer. The medication works by targeting and breaking down the estrogen receptor, which is a protein that helps some breast cancers grow. By doing this, ARV-471 aims to slow down or stop the cancer from growing, especially in patients whose cancer has continued to progress despite previous treatments.

  • Fulvestrant

    is a medication used to treat certain types of breast cancer. It works by blocking and breaking down the estrogen receptor, which is a protein that can help breast cancer cells grow. By interfering with this protein, fulvestrant aims to slow down or stop the growth of cancer cells. It is often used in patients who have already tried other treatments for their advanced breast cancer but need additional options to manage their disease.

What is already known about the treatment

  • ARV-471

    ARV-471 is an investigational medication administered orally, currently being studied in clinical trials for its potential use in treating advanced breast cancer. It is designed to target and degrade the estrogen receptor, which is often involved in the growth of certain types of breast cancer. This medication is classified as a selective estrogen receptor degrader (SERD) and aims to provide a more effective treatment option for patients whose cancer has progressed despite previous endocrine therapies. The main goal of ongoing research is to determine if ARV-471 can improve progression-free survival compared to existing treatments.

  • Fulvestrant

    Fulvestrant is a medication administered via intramuscular injection, commonly used in the treatment of hormone receptor-positive advanced breast cancer. It works by binding to estrogen receptors and promoting their degradation, thereby inhibiting the growth of cancer cells that rely on estrogen. Fulvestrant is classified as a selective estrogen receptor degrader (SERD) and is often used in patients whose cancer has progressed following other endocrine therapies. It is a well-established treatment option, with extensive documentation in medical literature supporting its efficacy in managing advanced breast cancer.

Investigated diseases

Advanced Breast Cancer – Advanced breast cancer refers to breast cancer that has spread beyond the initial tumor site to other parts of the body. It often involves the lymph nodes, bones, liver, lungs, or brain. The disease progresses as cancer cells grow and invade surrounding tissues, potentially forming new tumors in distant organs. Symptoms may include persistent pain, fatigue, and changes in breast appearance or function. The progression can vary, with some individuals experiencing rapid changes while others may have a slower course. The disease is typically characterized by its resistance to initial treatments and the need for ongoing management.
Trial detailsLast updated 2 Oct 2026
Age18+ yearsPhasePhase IIITrial ID2022-500544-38-00Protocol codeC4891001Estimated enrolment627 patientsSponsorPfizer Inc.

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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).