NCT07578649 · Pfizer
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
What this study is about
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.
View original scientific description
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. 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.
Interventions
BIOLOGICAL
PF-08634404
Solution for IV infusion
BIOLOGICAL
Pembrolizumab
Solution for IV infusion
DRUG
Standard of Care Chemotherapy
Solution for IV infusion
Primary outcome measures
Progression-Free Survival (PFS) using RECIST v1.1 as assessed by Blinded Independent Central Review (BICR)
Time frame: Approximately 36 months
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.
Who can participate
This study lists these criteria on ClinicalTrials.gov. A study coordinator reviews eligibility during screening — this page does not determine whether you qualify.
Inclusion criteria
- 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.
- 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.
Exclusion criteria
- 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.
- 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.
Where
- Jupiter, Florida
- Orlando, Florida
- Coon Rapids, Minnesota
- Edina, Minnesota
- Maple Grove, Minnesota
- Maplewood, Minnesota
- Woodbury, Minnesota
- Reno, Nevada
- Albany, New York
- White Plains, New York
- Centerville, Ohio
- Happy Valley, Oregon
And 22 more locations — see the full list below.
Collaborators
GOG Foundation, European Network of Gynaecological Oncological Trial Groups (ENGOT)
Related conditions & keywords
Frequently asked questions
What is a clinical trial?
A clinical trial is a research study that tests new medical treatments, drugs, devices, or procedures to determine their safety and effectiveness. Trials are carefully designed and monitored to protect participants while advancing medical knowledge.
Is it safe to participate?
Clinical trials follow strict safety guidelines and ethical standards. Trials must be reviewed and approved, and participants are closely monitored by medical professionals throughout the study. You can withdraw at any time if you choose.
Will I be compensated?
Many clinical trials offer compensation for your time, travel expenses, and inconvenience. The specific compensation varies by study and will be discussed during the screening process. All study-related medical care is typically provided at no cost to participants.
Will I receive a placebo instead of treatment?
When effective treatment exists, participants typically receive either the standard treatment plus the study intervention, or the standard treatment plus placebo. You would not be denied effective care. Placebos are primarily used when no proven treatment is available, or in addition to standard care. Your trial consent form will clearly explain what treatments you may receive.
Can I leave a trial if I change my mind?
Absolutely. Participation in clinical trials is completely voluntary. You have the right to withdraw from the study at any time, for any reason, without penalty or loss of benefits to which you are otherwise entitled.
How long does a clinical trial last?
Trial duration varies widely depending on the study design and purpose. Some trials last just a few weeks, while others may continue for months or years. The study coordinator will provide specific timeline information during your screening call.
Data: ClinicalTrials.gov · synced Oct 30, 2026 · Source of record for eligibility and locations