• Participants must have cytologically or histologically confirmed endometrial cancer that is recurrent or metastatic and/or resistant to standard therapies, or for which no standard therapy is available.Participants enrolled in the second stage of Cohort 1A, or into Cohort 3, 4, 6 and 7, must have histologically confirmed either i) endometrioid endometrial cancer or ii) endometrial carcinosarcoma with endometrioid epithelial component

• For Cohort 5: Participants must have histologically confirmed diagnosis of low-grade serous carcinoma of ovary, fallopian tube or peritoneum; original diagnosis of de novo low-grade serous carcinoma or original diagnosis of serous borderline tumor with subsequent diagnosis of low-grade serous carcinoma. Participants whose tumors contain both low-grade serous carcinoma and high-grade serous carcinoma are not eligible.

• Participants must have ER-positive disease, defined as ≥ 1 percent of tumor cell nuclei being immunoreactive by immunohistochemistry (IHC). If multiple analyses have been performed, judgment should be based on the most recent biopsy or pathology specimen analyzed in a CLIA-certified laboratory. For Cohort 5, participants are eligible regardless of ER positive or negative status.

• Participants must have measurable disease, defined as at least one lesion that can be accurately measured in at least one dimension (longest diameter to be recorded for non-nodal lesions and short axis for nodal lesions) as ≥20 mm with conventional techniques or as ≥10 mm with spiral CT scan, MRI, or calipers by clinical exam.

• Age ≥ 18 years

• ECOG performance status of 0 or 1

• Participants must have normal organ and bone marrow function as defined below:

‣ Absolute neutrophil count ≥ 1,500/mcL

⁃ Platelets ≥ 100,000/mcL

⁃ Total bilirubin ≤ 1.5 × institutional upper limit of normal (ULN). Patients with Gilbert's syndrome with a total bilirubin \</= 2.0 times ULN and direct bilirubin within normal limits are permitted.

⁃ AST(SGOT)/ALT(SGPT) ≤ 3× institutional ULN

⁃ Creatinine ≤ 1.5 × institutional ULN, OR

⁃ Creatinine clearance ≥ 60 mL/min/1.73 m2 for participants with creatinine levels above institutional normal.

• For cohorts 4, 5, 6 and 7, patients must not have remaining ovarian function to be included. Women who have ovarian function are eligible but must be placed on hormonal suppression.

• The effects of the study agents on the developing human fetus are unknown. For this reason, women of child-bearing potential must agree to use a medically approved contraceptive method during the treatment period and for 3 months following the last dose of study agent. Contraceptive methods may include an intrauterine device (IUD) or barrier method. If condoms are used as a barrier method, a spermicidal agent should be added as a double barrier protection. Should a woman become pregnant or suspect she is pregnant while she is participating in this study, she should inform her treating physician immediately. A negative serum pregnancy test is required for study entry from women of childbearing potential.

• Ability to understand and the willingness to sign a written informed consent document.

• Ability to swallow and retain oral medication.

• Participants can have received an unlimited number of prior therapies.

• Participants must have archival tissue available for analysis in the form of a formalin-fixed paraffin embedded (FFPE) block or unstained slides. Note: confirmation of availability of archival tissue is the only requirement for eligibility, archival tissue does not need to be received by the study team prior to enrollment

• For Cohorts 6 and 7, participants must have HbA1c ≤6.4% and fasting plasma glucose (FPG) ≤140 mg/dL.

• For Cohort 6 and 7, patients must have wildtype TP53 as assessed either by immunohistochemistry or any CLIA-certified next-generation sequencing assay.

• For Cohort 7, patients must have received prior CDK4/6 inhibitor therapy and developed disease progression as deemed by the investigator. Patients who have stopped CDK4/6 inhibitor therapy because of intolerance are ineligible.