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

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.