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Study of Pembrolizumab and Chemotherapy for Patients with HR+/HER2- Advanced 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 a type of breast cancer known as hormone receptor-positive, human epidermal growth factor receptor 2-negative (HR+/HER2-) breast cancer. This type of cancer can be locally recurrent, meaning it has come back in the same area, or metastatic, meaning it has spread to other parts of the body. The study is investigating the effects of a treatment called pembrolizumab, also known by its code name MK-3475 or Keytruda, in combination with chemotherapy. Pembrolizumab is a medication that helps the immune system fight cancer cells. The chemotherapy drugs being used in this study include paclitaxel, doxorubicin, capecitabine, and their variations, such as paclitaxel albumin-bound and doxorubicin hydrochloride, liposomal. Some participants will receive a placebo instead of pembrolizumab to compare the effects.

The purpose of this study is to see if pembrolizumab combined with chemotherapy is more effective than chemotherapy alone in treating this type of breast cancer. Participants will be randomly assigned to receive either the pembrolizumab and chemotherapy combination or a placebo and chemotherapy. The study will monitor how long participants live without the cancer getting worse and overall survival rates. The study will also look at the quality of life and any side effects experienced by participants.

Participants will receive the treatment through an intravenous (IV) infusion, which means the medication is given directly into a vein. The study will last for a period of time, during which participants will have regular check-ups and assessments to monitor their health and the progress of the treatment. The study aims to provide valuable information on the effectiveness and safety of pembrolizumab in combination with chemotherapy for treating HR+/HER2- breast cancer.

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, eligibility is confirmed based on specific criteria, including the type of breast cancer and previous treatments.

    A new biopsy may be required to confirm the cancer type and characteristics.

  2. Step 2

    Randomization

    Participants are randomly assigned to one of two groups: one receiving pembrolizumab plus chemotherapy, and the other receiving a placebo plus chemotherapy.

  3. Step 3

    Treatment administration

    Treatment involves intravenous administration of medications. Pembrolizumab is given as a solution for infusion.

    Chemotherapy may include drugs such as paclitaxel, doxorubicin, paclitaxel albumin-bound, and doxorubicin hydrochloride, liposomal.

    The specific chemotherapy regimen and schedule depend on the group assignment and individual treatment plan.

  4. Step 4

    Monitoring and assessments

    Regular monitoring is conducted to assess the response to treatment and any side effects.

    Assessments include imaging tests to evaluate tumor response and blood tests to monitor health status.

  5. Step 5

    Follow-up

    After completing the treatment phase, follow-up visits are scheduled to continue monitoring health and any long-term effects of the treatment.

    The duration of follow-up is determined by the study protocol and individual response to treatment.

Who can join the trial?

14 criteria

  • The patient must have **locally recurrent inoperable or metastatic HR+/HER2- breast cancer** that has not been treated with strong cancer drugs (cytotoxic chemotherapy) in a setting where the goal is not to cure the disease.
  • If the patient is a woman, she must not be pregnant or breastfeeding. She must either not be able to have children or use a very effective birth control method during the study and for a certain time after the last dose of the study drugs. She must also agree not to donate or store eggs for reproduction during this time.
  • The patient must have a **measurable disease** according to specific guidelines (RECIST 1.1), which means the cancer can be measured by doctors using scans or other methods.
  • If the patient is taking certain bone-strengthening medications (bisphosphonates or RANK ligand inhibitors), they must have been on a stable dose for at least 4 weeks before starting the study. If they need to start these medications during the screening period, a bone scan should be done before starting the study.
  • If the patient has **Hepatitis B**, they must have been on antiviral treatment for at least 4 weeks before the study and have no detectable virus in their blood.
  • If the patient has a history of **Hepatitis C**, they must have no detectable virus in their blood at the time of screening.
  • The patient must have tried hormone therapy before and now need chemotherapy. They must fit into one of several specific groups based on their previous treatments and how their disease has progressed.
  • The patient must have shown disease progression, meaning the cancer has grown or spread, as confirmed by a doctor or through a biopsy (a small sample of tissue taken for testing).
  • The patient must be a suitable candidate for chemotherapy as specified in the study protocol.
  • The patient must provide a new or recent biopsy sample from a cancerous area that has not been treated with radiation.
  • The patient must have a specific type of breast cancer confirmed by recent tests, with certain characteristics (PD-L1 CPS ≥1 and HR+/HER2-).
  • The patient must have a good general health status, as measured by a specific scale (ECOG performance status of 0 or 1), within 7 days before starting the study treatment.
  • The patient must have adequate organ function within 10 days before starting the study.
  • If the patient is male, he must agree to not donate sperm and either abstain from heterosexual intercourse or use contraception, including a condom, during the study and for at least 6 months after the last dose of chemotherapy.

Who cannot join the trial?

3 criteria

  • Patients who have already received **cytotoxic chemotherapy** for their breast cancer in a setting where the goal was not to cure the cancer cannot participate. **Cytotoxic chemotherapy** refers to drugs that kill cancer cells.
  • Patients with breast cancer that is not **HR+**/**HER2-** are excluded. **HR+** means the cancer grows in response to hormones, and **HER2-** means the cancer does not have too much of a protein called HER2.
  • Patients with breast cancer that is not **locally recurrent inoperable** or **metastatic** are excluded. **Locally recurrent inoperable** means the cancer has come back in the same area and cannot be removed by surgery. **Metastatic** means the cancer has spread to other parts of the body.
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Investigated drugs

  • Pembrolizumab

    is a medication used in this trial to help the body's immune system fight cancer. It works by blocking a specific protein that can stop the immune system from attacking cancer cells. This medication is being tested in combination with chemotherapy to see if it can improve outcomes for patients with certain types of breast cancer.

  • Chemotherapy

    refers to a group of cancer-fighting drugs used in this trial. These drugs work by killing or slowing the growth of cancer cells. In this study, chemotherapy is combined with pembrolizumab to evaluate if the combination is more effective than chemotherapy alone in treating breast cancer that is hormone receptor-positive and HER2-negative.

What is already known about the treatment

Pembrolizumab – Pembrolizumab is administered intravenously and is currently being studied in clinical trials for its effectiveness in treating certain types of breast cancer. It is primarily used for locally recurrent inoperable or metastatic hormone receptor-positive, HER2-negative breast cancer that has not been previously treated with chemotherapy in a noncurative setting. Pembrolizumab works by blocking a protein called PD-1 on the surface of immune cells, which helps the immune system recognize and attack cancer cells. It is classified as an immune checkpoint inhibitor, a type of immunotherapy that enhances the body's natural defenses to fight cancer.

Investigated diseases

Locally Recurrent Inoperable or Metastatic HR+/HER2- Breast Cancer – This type of breast cancer is characterized by the recurrence of cancer cells in the breast or nearby areas after initial treatment, and it cannot be removed surgically. It is hormone receptor-positive (HR+) and human epidermal growth factor receptor 2-negative (HER2-), meaning the cancer cells grow in response to hormones but do not have excess HER2 protein. The disease can also spread to other parts of the body, known as metastasis. It progresses as cancer cells continue to grow and spread, affecting various organs and tissues. The progression can lead to symptoms such as pain, fatigue, and changes in the affected breast or other areas. This type of breast cancer has not been previously treated with cytotoxic chemotherapy in a noncurative setting.
Trial detailsLast updated 2 Oct 2026
Age18+ yearsPhasePhase IIITrial ID2023-506752-24-00Protocol codeMK-3475-B49Estimated enrolment481 patientsSponsorMerck Sharp & Dohme LLC

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