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Endometrial NeoplasmsPhase 3NCT07578649

Symbiotic-GYN-18: A Study to Learn About the Study Medicine Called PF-08634404 in Combination With Chemotherapy in Adult Participants With Advanced or Recurrent MMR-proficient Endometrial Cancer

A Phase 3 study testing PF-08634404 and Pembrolizumab in people with Endometrial Neoplasms and Endometrial Cancer, run by Pfizer at 43 sites in 4 countries.

Not yet recruiting

Opening soon. The study is approved but enrolment has not started yet. Sites may already take enquiries.

Sites and contacts
Official record
Search all trials

Trial summary

This study is being conducted to assess whether the study medicine PF 08634404, given in combination with chemotherapy, improves outcomes compared with another medicine called pembrolizumab plus chemotherapy. Read more about this study

Who is it for?
Ages 18 years and older, women only
Conditions the study is for
Endometrial Neoplasms, Endometrial Cancer
What is being tested?
PF-08634404 and Pembrolizumab
Type of treatment
Injection or infusion
Could I receive a placebo?
No, everyone receives an active treatment
How many people
600 participants
Where
43 sitesin 4 countries
Study dates
9 Oct 2026to 30 Jan 2031
Phase
Phase 3
Are there results?
Not yet: the study is under way

Key requirements

Who can take part, as listed by the sponsor. Only the study team can confirm whether you are eligible, so take this list to your doctor.

  • Ages 18 years and older
  • Women only
  • No healthy volunteers
  • Adult, Older adult

Who may be able to join

  • Women ≥18 years of age who are confirmed not pregnant at screening.
  • Histologically or cytologically confirmed endometrial cancer that is recurrent or advanced; carcinosarcomas are eligible but pure sarcomas are excluded.
  • Newly diagnosed FIGO Stage III disease with measurable disease per RECIST v1.1, newly diagnosed FIGO Stage IV disease with or without measurable disease, or recurrent disease with or without measurable disease for which curative treatment with surgery and/or radiotherapy is unlikely.
  • For participants with recurrent disease, prior adjuvant systemic anti-cancer therapy is allowed if relapse occurred more than 6 months after the last dose.
  • Must provide tumor tissue for prospective central assessment of MMR and p53 status.
  • Proficient mismatch repair (pMMR) endometrial cancer as determined by central testing.
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  • Eastern Cooperative Oncology Group (ECOG) performance status of 0 to 1.
  • Life expectancy of at least 12 weeks.
  • Adequate organ function as defined in the protocol.

Who cannot join

  • Prior systemic therapy for first-line advanced or recurrent endometrial cancer.
  • Prior immunotherapy or anti-angiogenic therapy.
  • Deficient mismatch repair (dMMR) endometrial cancer by central testing.
  • Active or untreated central nervous system (CNS) metastases; participants with previously treated and clinically stable brain metastases may be eligible if not requiring steroids and without evidence of progression.
  • Clinically significant risk of bleeding or fistula, including a history of severe bleeding disorders.
  • History of another malignancy within 3 years, except for cancers with negligible risk of recurrence or death.
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  • History of allogeneic organ or hematopoietic stem cell transplantation; active autoimmune disease requiring systemic treatment within the past 2 years; or history of immunodeficiency
  • Interstitial lung disease, pneumonitis, or clinically significant pulmonary disease
  • Uncontrolled or significant cardiovascular, metabolic, renal, hepatic, or vascular disease
  • Active or uncontrolled infection.
  • Recent major surgery or severe trauma within protocol-defined washout periods.

Trial locations and contacts

43 sites in 4 countries. Contact the study team or a site near you to ask about taking part.

Pfizer CT.gov Call Center contact

1-800-718-1021

ClinicalTrials.gov_Inquiries@pfizer.com

43 sites in 4 countries

United States36 sites

  • Texas Oncology - West Texas

    Abilene, Texas, 79606

  • Texas Oncology-West Texas

    Amarillo, Texas, 79124

  • Texas Oncology - Central South

    Austin, Texas, 78731

  • Texas Oncology - Central South

    Austin, Texas, 78745

  • Texas Oncology - Central South

    Austin, Texas, 78758

  • Miami Valley Hospital South

    Centerville, Ohio, 45459

  • Virginia Oncology Associates

    Chesapeake, Virginia, 23320

  • Minnesota Oncology Hematology, PA

    Coon Rapids, Minnesota, 55433

  • Minnesota Oncology Hematology, PA

    Edina, Minnesota, 55435

  • Texas Oncology-West Texas

    El Paso, Texas, 79902

  • Texas Oncology - West Texas

    El Paso, Texas, 79915

  • Texas Oncology - West Texas

    El Paso, Texas, 79938

  • Northwest Cancer Specialists, P.C.

    Happy Valley, Oregon, 97015

  • Texas Oncology - Central South

    Harlingen, Texas, 78550

  • Minnesota Oncology Hematology, P.A.

    Hudson, Wisconsin, 54016

  • US Oncology Investigational Products Center (IPC)

    Irving, Texas, 75063

  • Jupiter Medical Center/ Anderson Family Cancer Institute

    Jupiter, Florida, 33458

  • Minnesota Oncology Hematology, PA

    Maple Grove, Minnesota, 55369

  • Minnesota Oncology Hematology, PA

    Maplewood, Minnesota, 55109

  • Texas Oncology - Central South

    McAllen, Texas, 78503

  • Texas Oncology-West Texas

    Midland, Texas, 79701

  • Sarah Cannon Research Institute- Pharmacy

    Nashville, Tennessee, 37203

  • SCRI Oncology Partners

    Nashville, Tennessee, 37203

  • Virginia Oncology Associates

    Newport News, Virginia, 23606

  • Virginia Oncology Associates

    Norfolk, Virginia, 23502

  • Texas Oncology - West Texas

    Odessa, Texas, 79761

  • Northwest Cancer Specialists, P.C.

    Portland, Oregon, 97227

  • The Center of Hope

    Reno, Nevada, 89511

  • Virginia Oncology Associates

    Suffolk, Virginia, 23435

  • Northwest Cancer Specialists, P.C.

    Tigard, Oregon, 97223

  • Northwest Cancer Specialists, P.C.

    Vancouver, Washington, 98684

  • Texas Oncology - Central South

    Waco, Texas, 76712

  • Texas Oncology - Central South

    Weslaco, Texas, 78596

  • Texas Oncology-West Texas

    Wichita Falls, Texas, 76310

  • Virginia Oncology Associates

    Williamsburg, Virginia, 23188

  • Minnesota Oncology Hematology, PA

    Woodbury, Minnesota, 55125

Other trials in United States

Japan5 sites

  • Hyogo Cancer Center

    Akashi, Hyōgo, 673-8558

  • Saitama Medical University International Medical Center

    Hidaka, Saitama, 350-1298

  • Cancer Institute Hospital of JFCR

    Koto-ku, Tokyo, 135-8550

  • Niigata Cancer Center Hospital

    Niigata, 951-8566

  • Sapporo Medical University Hospital

    Sapporo, Hokkaido, 060-0061

Other trials in Japan

Australia1 site

  • Bayside Health - Peninsula University Hospital

    Frankston, Victoria, 3199

Other trials in Australia

Taiwan1 site

  • Taichung Veterans General Hospital

    Taichung, 407

Other trials in Taiwan

About this study

Official title: AN INTERVENTIONAL PHASE 3, OPEN LABEL, RANDOMIZED STUDY TO EVALUATE EFFICACY AND SAFETY OF PF-08634404 IN COMBINATION WITH CHEMOTHERAPY VERSUS PEMBROLIZUMAB IN COMBINATION WITH CHEMOTHERAPY IN ADULT PARTICIPANTS WITH ADVANCED OR RECURRENT MISMATCH REPAIR PROFICIENT ENDOMETRIAL CANCER

This study is being conducted to assess whether the study medicine PF 08634404, given in combination with chemotherapy, improves outcomes compared with another medicine called pembrolizumab plus chemotherapy. Chemotherapy is a type of cancer treatment that uses medicines to destroy cancer cells or stop them from growing.

Our bodies have a built-in DNA "spell-checker," called the mismatch repair (MMR) system, that fixes genetic mistakes. In most endometrial cancers, this system works normally, and these cancers are called MMR-proficient (pMMR). However, pMMR tumors are harder for the immune system to recognize and attack. When endometrial cancer has spread beyond the uterus or comes back after previous treatment, it is called advanced or recurrent endometrial cancer. This study is for adults with mismatch repair-pMMR advanced or recurrent endometrial cancer.

Read more

Participants must meet key criteria, including:

  • Women who are 18 years or older, and not pregnant at the time of joining the study
  • pMMR endometrial cancer only
  • Measurable Stage III disease, Stage IV disease (with or without measurable disease) per FIGO staging, a system doctors use to describe how far cancer has spread in the body, or recurrent (with or without measurable disease) endometrial cancer
  • Has not received chemotherapy except for chemotherapy given after the main surgery and more than 6 months before relapse
  • Be in good enough health to receive study treatment. Approximately 600 adult women will be enrolled. Each participant will be randomly assigned (like a flip of the coin) to one of two treatment groups, with about half in each group. The study is open, meaning both the doctors and participants know what treatment is being given. Participants will receive their assigned treatment through intravenous infusions (medicine is given directly into a vein). The treatment will be given in cycles.

Experimental Group will receive new study medicine called PF-08634404 plus chemotherapy. It will be followed by PF 08634404 alone for up to 2 years (35 cycles).

Control Group will receive an approved medicine called pembrolizumab plus chemotherapy. It will be followed by pembrolizumab alone for up to 2 years (20 cycles).

The study will include regular visits for:

  • Participants will have regular visits to the study site for treatment, health checks, and tests.
  • After stopping treatment, participants will come for a final visit within a month to check their health and review any reactions.
  • Follow-up will continue every 12 weeks by phone or in person or by reviewing health records. This helps check health and any new treatments.
  • Tests will be done every 9 weeks during the first 104 weeks to see how the cancer is responding. After that, tests will be done every 12 weeks.
Being tested
PF-08634404, Pembrolizumab, Standard of Care Chemotherapy
Keywords
Recurrent Endometrial Carcinoma, Endometrial Neoplasms, Advanced Endometrial Carcinoma, Advanced or Recurrent Endometrial Cancer, pMMR
Medical subject headings
Endometrial Neoplasms

What participants receive

What participants receive. In a randomised study each person is assigned to one group by chance.

  • PF-08634404Biological

    Solution for IV infusion

  • PembrolizumabBiological

    Also called keytruda

    Solution for IV infusion

  • Standard of Care ChemotherapyDrug

    Solution for IV infusion

Study groups in NCT07578649
Study groupRoleWhat they receive
PF-08634404 plus ChemotherapyExperimentalPF-08634404 plus Chemotherapy, followed by PF-08634404 maintenance therapy
Receives: Biological: PF-08634404; Drug: Standard of Care Chemotherapy
Pembrolizumab plus ChemotherapyActive comparatorPembrolizumab plus Chemotherapy, followed by Pembrolizumab maintenance therapy
Receives: Biological: Pembrolizumab; Drug: Standard of Care Chemotherapy

What is being measured

The primary outcome is the main question the study is designed to answer.

  1. Progression-Free Survival (PFS) using RECIST v1.1 as assessed by Blinded Independent Central Review (BICR)

    PFS by BICR is defined as the time from the date of randomization to the date of first documented disease progression per RECIST v1.1 as assessed by BICR, or death due to any cause, whichever occurs first.

    Measured: Approximately 36 months

Secondary outcomes (11)

  1. Overall Survival (OS)

    OS is defined as the time from the date of randomization to the date of death due to any cause.

    Measured: Approximately 56 months

  2. PFS using RECIST v1.1 as assessed by investigator

    PFS by investigator is defined as the time from the date of randomization to the date of first documented disease progression per RECIST v1.1 as assessed by investigator, or death due to any cause, whichever occurs first. PFS by investigator will be analyzed with the same methodology as for PFS by BICR.

    Measured: Approximately 36 months

  3. Objective Response Rate (ORR) as assessed by BICR and investigator

    Proportion of participants with confirmed Complete Response (CR) or Partial Response (PR) per RECIST v1.1, assessed by BICR and by investigator

    Measured: Approximately 56 months

  4. Duration of Response (DoR) as assessed by BICR and investigator

    Time from first documented CR or PR to disease progression or death, per RECIST v1.1, assessed by BICR and by investigator

    Measured: Approximately 56 months

  5. Number of participants with treatment-emergent adverse events

    AEs as characterized by type, frequency, intensity as graded by NCI CTCAE version 5.0, timing, seriousness, and relationship to study intervention(s)

    Measured: Through end of the study and up to approximately 56 months

  6. Number of participants with laboratory abnormalities

    Laboratory abnormalities as characterized by type, frequency, severity (as graded by NCI CTCAE version 5.0), and timing. For laboratory tests without CTCAE grade definitions, results will be categorized as normal, high, low, or not done and be listed.

    Measured: Through end of the study and up to approximately 56 months

  7. Serum concentrations of PF-08634404

    Pre-dose and post-dose serum concentrations of PF-08634404

    Measured: Through end of the study and up to approximately 56 months

  8. Incidence of ADA against PF-08634404

    Incidence of anti-drug antibodies (ADA) to PF-08634404

    Measured: Through end of the study and up to approximately 56 months

  9. Change from baseline in the global health status/quality of life (QoL) and physical functioning scale of the European Organisation for Research and Treatment of Cancer Quality of Life Questionnaire-Core 30 (EORTC QLQ-C30)

    The EORTC QLQ-C30 is a questionnaire for quantitative measure of health-related quality of life pertinent to participants with a broad range of cancers who are participating in international clinical trials. The core instrument is a 30-item questionnaire consisting of the following:

    • 5 Functional scales (physical, role, cognitive, emotional, social)
    • 3 Symptom scales (fatigue, pain, nausea, and vomiting, shortness of breath, loss of appetite, sleep disturbance, constipation, diarrhea) and financial impact of the disease
    • 2 Global items (global health status, overall HRQoL) All of the scales and single-item measures range in score from 0 to 100. High scale score represents a higher response level.

    Measured: Baseline, up to approximately 56 months

  10. Change from baseline in the back pain/pelvis pain, GI symptoms, and urological symptoms scales of the EORTC QLQ EN24

    The Endometrial Cancer Module (EORTC QLQ-EN24) is a disease-specific measure that is supplemental to the EORTC QLQ-C30 to capture patient's experiences with endometrial cancer-specific symptoms and impacts. The recall period is the past week. The 24-item questionnaire consists of the following:

    • Symptom scales/items (Lymphoedema, urological symptoms, gastrointestinal symptoms, poor body image, and sexual/vaginal problems, pain in back and pelvis, tingling/numbness, muscular pain, hair loss, and taste change)
    • Functional scales (sexual interest, sexual activity, and sexual enjoyment)

    Higher scores for functional scales represent high level of functioning, while higher scores for symptoms scales represent higher levels of symptoms/problems.

    Measured: Baseline, up to approximately 56 months

  11. Time to definitive deterioration in the global health status/QoL and physical functioning scale of the EORTC QLQ-C30.

    The European Organisation for Research and Treatment of Cancer Quality of Life-Core 30 Questionnaire (EORTC QLQ-C30), is a validated 30-item self-administered core questionnaire designed to assess HRQoL, functioning, and symptoms in all cancer patients or survivors.

    Time to deterioration is defined as time from baseline (defined as day 1 of cycle 1 before first application of maintenance therapy) to the date of the first clinically meaningful deterioration i.e. a decrease by ≥10 points for the functional scales and an increase by ≥ 10 points for the symptom scales or death in:

    • Physical functioning score
    • Role functioning score

    Measured: Approximately 56 months

Timeline

From the start of the study to its completion; the mark is today. Estimated dates are the sponsor’s plan.

  1. First posted11 May 2026
  2. Study start9 Oct 2026 (estimated)
  3. Primary completion1 Jun 2029 (estimated)
  4. Study completion30 Jan 2031 (estimated)

Resources

More details

For doctors and researchers: how the study is designed, who runs it, and its registry IDs.

Study design
Study type
Interventional
Phase
Phase 3
Primary purpose
Treatment
Allocation
Randomised
Intervention model
Parallel groups
Masking
None (open label)
Enrolment
600 participants (estimated)
IDs, dates and publications
ClinicalTrials.gov ID
NCT07578649
Sponsor's protocol ID
C6461018
Other IDs
2026-525584-40-00, GOG-3145, ENGOT-en37, APGOT-EN6
Status last verified
Oct 2026
First submitted
5 May 2026
Last updated
8 Oct 2026
Results posted
No
Data monitoring committee
Yes
FDA-regulated drug
Yes
FDA-regulated device
No
Individual data sharing
Yes: Pfizer will provide access to individual de-identified participant data and related study documents (e.g. protocol, Statistical Analysis Plan (SAP), Clinical Study Report (CSR)) upon request from qualified researchers, and subject to certain criteria, conditions, and exceptions. Further details on Pfizer's data sharing criteria and process for requesting access can be found at: https://www.pfizer.com/science/clinical\_trials/trial\_data\_and\_results/data\_requests.

Questions about this trial

What is this clinical trial studying?

A Phase 3 study testing PF-08634404 and Pembrolizumab in people with Endometrial Neoplasms and Endometrial Cancer, run by Pfizer at 43 sites in 4 countries.

The full registered description is in the About this study section and the official record.

Who may be eligible to take part?

The sponsor lists 9 inclusion and 11 exclusion criteria. Eligibility is decided by the study team after screening, so read the full criteria and contact a listed site.

Is this clinical trial currently recruiting?

The record says: opening soon, as of the sponsor's last update on 8 Oct 2026. Status can change between updates, so confirm with the study contact before making plans.

Where is the study taking place?

The record lists 43 sites in United States, Japan, Australia, Taiwan. Whether a site is taking part right now should be confirmed with that site. See every site.

What are the possible benefits and risks?

They depend on the study and the treatment, and no study can promise a benefit. The study team explains the known risks during informed consent, before anyone joins; the record itself does not list them.

What does this phase mean?

Phase 3 studies compare the treatment with the current standard treatment or a placebo in a large group, to confirm how well it works and watch for side effects.

Not every study follows the same path, and some studies (observational studies, device studies) have no phase.

Are results available for this study?

This study is still under way. Results are not available in the source record yet.

How can a doctor refer a patient or contact the research team?

Contact Pfizer CT.gov Call Center (1-800-718-1021, ClinicalTrials.gov_Inquiries@pfizer.com), or a site near the patient. AzTrials does not enrol participants or take referrals.

What does the primary outcome measure?

Progression-Free Survival (PFS) using RECIST v1.1 as assessed by Blinded Independent Central Review (BICR) (time frame: Approximately 36 months). It is what the study was designed to measure, not a finding.

Where can I read the original study information?

On the ClinicalTrials.gov record for NCT07578649.

Does a listing mean the treatment is approved or proven to work?

No. A listing means the study is registered. It does not show that the treatment is safe, works, or is approved by a regulator.

How often is this information updated?

AzTrials copies changed records from ClinicalTrials.gov every night and reloads the whole registry every week. The sponsor last updated this record on 8 Oct 2026.

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