Skip to content
Clinical Trials – home

Rare diseases

Investigational molecules

Locations

Our offerNewsroom

Not recruiting

Study of PF-07220060 and PF-07104091 with Endocrine Therapy for Patients with Advanced HR-positive HER2-negative Breast Cancer

Fast replyRegistered drug
Clinical Trials Concierge

Prefer not to search? Our Concierge searches the trials for you.

What is this trial about?

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

This clinical trial is focused on studying the effects of a new treatment for people with advanced solid tumors, including a specific type of breast cancer known as HR-positive HER2-negative metastatic or advanced breast cancer. The study involves a combination of medications, including two investigational drugs, PF-07220060 and PF-07104091, along with standard endocrine therapies like fulvestrant and letrozole. These medications are being tested to see how safe and tolerable they are when used together, as well as to understand their potential to fight cancer.

The purpose of the study is to evaluate the safety and tolerability of these medications in participants with advanced solid tumors. The study is divided into two parts. In the first part, participants will receive increasing doses of PF-07220060 and PF-07104091 to determine the most suitable dose for further testing. In the second part, the combination of these drugs with endocrine therapies will be tested in participants with HR-positive HER2-negative advanced or metastatic breast cancer. The study will monitor participants for any side effects and how their bodies respond to the treatment over a period of up to four months.

Participants will take the medications in the form of tablets or injections, depending on the specific drug. The study aims to gather information on how the drugs are processed in the body and their impact on the cancer. This research is important for developing new treatment options for people with advanced cancers, particularly those who have limited options available. The study is expected to continue until the end of 2026.

The research process

The trial runs in 7 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 solid tumors.

    Participants must have a measurable lesion that has not been previously treated with radiation.

  2. Step 2

    Initial assessment

    An initial assessment is conducted to evaluate the current health status, including vital signs and laboratory tests.

    This assessment helps establish a baseline for monitoring throughout the study.

  3. Step 3

    Treatment phase 1

    The first phase involves the administration of increasing doses of PF-07220060 and PF-07104091 to determine the maximum tolerated dose.

    Medications are taken orally in tablet form.

  4. Step 4

    Monitoring and evaluation

    Participants are closely monitored for any side effects or adverse reactions.

    Regular check-ups include laboratory tests and assessments of vital signs.

  5. Step 5

    Treatment phase 2

    In the second phase, the combination therapy includes PF-07220060, PF-07104091, and endocrine therapy with either fulvestrant or letrozole.

    Fulvestrant is administered as an intramuscular injection, while letrozole is taken orally.

  6. Step 6

    Ongoing assessment

    Continuous assessment of safety and tolerability is conducted throughout the study.

    Participants undergo regular evaluations to monitor the effectiveness of the treatment.

  7. Step 7

    Completion of study

    The study is estimated to conclude by December 29, 2026.

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

Who can join the trial?

7 criteria

  • Participants must be **18 years or older**.
  • Must have a **diagnosis of a locally advanced or metastatic solid tumor**. This means the cancer has spread and cannot be removed by surgery.
  • Must have a **lesion that can be evaluated**. A lesion is an area of abnormal tissue.
  • For those in the expansion group, there must be at least **one measurable lesion** that has not been treated with radiation before. A measurable lesion is a tumor that can be measured in size.
  • The cancer type must be **HR-positive HER2-negative** or **HR-positive HER2-positive**. HR-positive means the cancer grows in response to hormones. HER2-negative or HER2-positive refers to whether the cancer has a protein that promotes growth.
  • Must have an **advanced solid tumor** or **metastatic disease**. Metastatic disease means the cancer has spread to other parts of the body.
  • Must have an **ECOG PS of 0 or 1**. ECOG PS is a scale that measures how well a person can perform daily activities. A score of 0 means fully active, and 1 means some symptoms but still able to do light work.

Who cannot join the trial?

6 criteria

  • Patients with a type of breast cancer that is not HR-positive or HER2-negative. HR-positive means the cancer grows in response to hormones. HER2-negative means the cancer does not have high levels of a protein called HER2.
  • Patients who do not have metastatic or advanced breast cancer. Metastatic means the cancer has spread to other parts of the body. Advanced means the cancer is in a later stage and may be more difficult to treat.
  • Patients who are not within the specified age range for the study.
  • Patients who are not part of the specified clinical trial group.
  • Patients who are not female or male, as both genders are included in the study.
  • Patients who are considered part of a vulnerable population, which means they may need special protection or care.
Clinical Trials Concierge

Prefer not to search? Our Concierge searches the trials for you.

Tell us about your condition – we search every trial in Europe and connect you with the right site.

We usually reply within a few days

Verified sites

All sites with verified contact details – recruitment status may not be available; ask directly

Trial locations

Where you can join this trial

Countries are shaded by recruitment status. Click a recruiting country to ask about joining there.

Not recruiting
Not finding your country?

Not sure what to do next?

Joining a clinical trial can seem overwhelming. We guide you step by step, so you know exactly what to expect and how we support you through the process.

See the full process and FAQ

Investigated drugs

  • PF-07220060

    is an investigational medication being studied for its potential to treat advanced solid tumors. It is being tested in combination with other treatments to evaluate its safety, tolerability, and effectiveness in shrinking or controlling tumors.

  • PF-07104091

    is another investigational medication used in this study. It is combined with PF-07220060 to see how well the two medications work together in treating advanced solid tumors. The study aims to find the best dose that patients can tolerate while still being effective.

  • Fulvestrant

    is a type of endocrine therapy used in this trial. It is a hormone therapy that works by blocking the effects 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 also an endocrine therapy included in the study. It is used to lower estrogen levels in the body, which can help prevent the growth of hormone receptor-positive breast cancer cells. This medication is being tested in combination with the investigational drugs to assess its effectiveness in treating advanced breast cancer.

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 advanced solid tumors, specifically HR-positive HER2-negative metastatic or advanced breast cancer. It is in the early stages of research, focusing on its safety and effectiveness when used in combination with other treatments. The main therapeutic indication is for advanced breast cancer. At the molecular level, it works by targeting specific pathways that are involved in cancer cell growth and survival. It is classified as an investigational drug, meaning it is still under study and not yet approved for general medical use.

  • PF-07104091

    This medication is also administered orally and is being evaluated in clinical trials alongside PF-07220060 for its potential in treating advanced solid tumors, particularly HR-positive HER2-negative metastatic or advanced breast cancer. The current status is investigational, as it is being tested for safety and efficacy in combination therapies. Its primary therapeutic use is aimed at advanced breast cancer. The mechanism of action involves inhibiting certain proteins that contribute to cancer cell proliferation. Like PF-07220060, it is classified as an investigational drug, pending further research and approval.

Investigated diseases

Hormone Receptor-Positive, HER2-Negative Metastatic/Advanced Breast Cancer – This type of breast cancer is characterized by the presence of hormone receptors, meaning the cancer cells grow in response to hormones like estrogen or progesterone. It is HER2-negative, indicating that the cancer cells do not have an excess of the HER2 protein on their surface. This form of breast cancer can spread beyond the breast to other parts of the body, such as bones, liver, or lungs, which is referred to as metastatic or advanced stage. The progression of the disease can vary, with some patients experiencing slow growth and others facing more rapid advancement. The cancer's behavior is influenced by the hormone receptor status, which can guide treatment decisions. Understanding the hormone receptor and HER2 status is crucial for determining the most effective management strategies.
Trial detailsLast updated 2 Oct 2026
Age18+ yearsPhasePhase IITrial ID2023-509504-15-00Protocol codeC4391002Estimated enrolment240 patientsSponsorPfizer Inc.

sourced from the EU Clinical Trials Register and site verification

Want to learn more about this trial or check if you can participate?

Clinical Trials Concierge

Prefer not to search? Our Concierge searches the trials for you.

Tell us about your condition – we search every trial in Europe and connect you with the right site.

ClinicalTrials.eu

Every clinical trial in Europe, in plain language.

Explore the full ecosystem of clinical research in Europe.

Search trials

Legal notice · Published by CTIN POLAND sp. z o.o., ul. rtm. Witolda Pileckiego 67/109, 02-781 Warsaw, Poland · KRS 0001111334 · REGON 528919042 · NIP 9512598637

© 2026 Clinical Trials EU – European Clinical Trials Information Network

GDPR compliance, ISO 9001 and ISO 27001 certified (LL-C Certification)

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).