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Study of PF-07220060 and Letrozole for Postmenopausal Women with HR-Positive, HER2-Negative 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, HER2-negative breast cancer. This type of cancer is characterized by the presence of hormone receptors and the absence of a protein called HER2 on the surface of the cancer cells. The study is being conducted in postmenopausal women who are 18 years or older. The treatment being tested involves a combination of two medications: PF-07220060 and letrozole. PF-07220060 is a new investigational drug, while letrozole is a medication commonly used to treat breast cancer by lowering estrogen levels in the body.

The purpose of the study is to compare the effects of the combination of PF-07220060 and letrozole with letrozole alone. Participants will receive either the combination treatment or letrozole by itself. The study will last for a period of two weeks, during which the effects of the treatments on the cancer cells will be closely monitored. The main focus is on observing changes in a specific protein called Ki-67, which is associated with cell growth, in the tumors after the treatment period.

Participants will be required to undergo certain procedures, including biopsies, which involve taking small samples of the tumor tissue to study the effects of the treatment. The study aims to provide valuable information on how the combination of PF-07220060 and letrozole affects breast cancer cells compared to letrozole alone, potentially leading to improved treatment options for this type of breast cancer in the future.

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, you will be informed about the trial's purpose and procedures. You will be asked to provide consent to participate.

    You will undergo a screening process to confirm eligibility, which includes confirming your postmenopausal status and the specific type of breast cancer.

  2. Step 2

    Initial assessments

    You will have a baseline biopsy, which involves taking a small sample of your tumor tissue for analysis.

    Other initial assessments may include blood tests and imaging to establish a starting point for your treatment.

  3. Step 3

    Treatment phase

    You will be randomly assigned to one of two groups: one group will receive PF-07220060 plus letrozole, and the other group will receive letrozole alone.

    Letrozole is taken orally as a 2.5 mg film-coated tablet. The dosage and frequency of PF-07220060 will be explained to you by the study team.

    The treatment will last for 14 days, during which you will continue to take the medication as instructed.

  4. Step 4

    Mid-treatment evaluation

    On Day 14, you will undergo another biopsy to assess changes in the tumor.

    Blood samples will be taken to measure the concentration of PF-07220060 in your system and to check for any changes in your condition.

  5. Step 5

    Monitoring and follow-up

    Throughout the trial, you will be monitored for any side effects or adverse events. It is important to report any new symptoms or concerns to the study team.

    You will have regular follow-up visits to assess your health and the effects of the treatment.

  6. Step 6

    End of trial

    At the end of the trial, you will have a final assessment to evaluate the overall impact of the treatment.

    The study team will discuss the results with you and provide guidance on the next steps for your care.

Who can join the trial?

7 criteria

  • Participants must be female and at least 18 years old or the minimum age of consent according to local regulations.
  • Participants must be in postmenopause, which means they have stopped having menstrual periods, either naturally or due to surgery.
  • Participants must have a diagnosis of hormone receptor-positive, HER2-negative breast cancer. This means the cancer grows in response to hormones but does not have too much of the HER2 protein.
  • Participants must have a Ki-67 score of 10% or higher. Ki-67 is a measure of how quickly cancer cells are growing.
  • Participants must have a specific type of breast cancer that is unilateral (affecting one breast), invasive (cancer has spread into surrounding breast tissue), and classified as T1c-T4c, N0-N2, M0 according to the AJCC Version 8. This classification describes the size and extent of the cancer.
  • Participants must have an ECOG performance status of 0 or 1. This is a scale used to assess how well a person can perform daily activities, with 0 being fully active and 1 being restricted in physically strenuous activity but able to carry out light work.
  • Participants must be willing to undergo a baseline biopsy (a procedure to remove a small sample of tissue for testing) if it has not been done already, and an on-treatment biopsy during the study.

Who cannot join the trial?

7 criteria

  • Patients with any other type of cancer besides hormone receptor-positive, HER2-negative breast cancer cannot participate.
  • Men are not eligible to participate in this study.
  • Individuals under the age of 18 or over the age of 65 are not eligible.
  • Pregnant or breastfeeding women cannot participate.
  • Patients who have received any other cancer treatment within the last 2 weeks are not eligible.
  • Patients with severe or uncontrolled medical conditions that could interfere with the study are not eligible.
  • Patients who are unable to comply with the study procedures or follow-up visits are not eligible.
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Investigated drugs

  • PF-07220060

    is an experimental medication being studied for its potential to treat breast cancer. In this trial, it is being tested in combination with another medication to see if it can help reduce the growth of cancer cells in women who have a specific type of breast cancer. This medication is still under investigation, which means researchers are trying to understand how well it works and how safe it is for patients.

  • Letrozole

    is a medication commonly used to treat breast cancer in postmenopausal women. It works by lowering the levels of estrogen in the body, which can help slow down or stop the growth of certain types of breast cancer cells that need estrogen to grow. In this trial, letrozole is being used both alone and in combination with another medication to see how effective it is in reducing cancer cell growth.

What is already known about the treatment

  • PF-07220060

    This medication is administered orally and is currently being studied in clinical trials for its potential use in treating hormone receptor-positive, HER2-negative breast cancer. It is being evaluated in combination with letrozole, a well-known breast cancer treatment, to see if it can enhance the effects of letrozole. PF-07220060 works by targeting specific proteins in cancer cells that help them grow, aiming to slow down or stop the progression of the disease. It falls under the category of targeted cancer therapies, which are designed to interfere with cancer cell growth at the molecular level.

  • Letrozole

    Letrozole is an oral medication that is already widely used in the treatment of hormone receptor-positive, HER2-negative breast cancer, particularly in postmenopausal women. It works by reducing the levels of estrogen in the body, which can help slow or stop the growth of certain types of breast cancer cells that need estrogen to grow. Letrozole is classified as an aromatase inhibitor, a type of hormone therapy that is effective in managing breast cancer by blocking the production of estrogen.

Investigated diseases

Hormone Receptor-Positive, HER2-Negative Breast Cancer – This type of breast cancer is characterized by the presence of receptors for hormones like estrogen or progesterone, but it does not have an excess of the HER2 protein. The cancer cells grow in response to these hormones, which can influence the progression of the disease. It typically begins in the breast tissue and can spread to nearby lymph nodes or other parts of the body. The growth rate of this cancer can vary, and it may progress slowly or more rapidly depending on various factors. The absence of HER2 overexpression means that certain targeted therapies are not applicable. Understanding the hormone receptor status is crucial for determining the course of the disease.
Trial detailsLast updated 2 Oct 2026
Age18+ yearsPhasePhase IITrial ID2024-512848-30-00Protocol codeC4391025Estimated enrolment131 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).