The purpose of this study is to determine the efficacy and safety of Pembrolizumab in combination with Lenvatinib in recurrent, mismatch repair-proficient endometrial cancer after failure of first-line therapy with a platinum-based doublet chemotherapy and immunotherapy.

Inclusion Criteria:

1. Histologically confirmed recurrent endometrial carcinoma, including serous, endometrioid, carcinosarcoma, clear cell subtypes, with measurable disease per RECIST 1.1 criteria.

2. Mismatch repair (MMR) proficient status confirmed by IHC (Immunohistochemistry) or molecular testing.

3. Patients must have failed first-line therapy with platinum based doublet with prior immunotherapy.

4. Patient must have completed next-generation sequencing on either primary or recurrent tumor.

5. Eastern Cooperative Oncology Group (ECOG) performance status of 0 - 3.

6. Age ≥ 18 years.

7. Female participants must be of non-childbearing potential or for females of child bearing potential (FOCBPs), must agree to use contraception as described in Section 5.6. FOCBPs must not be pregnant or breastfeeding.

8. At least one measurable lesion according to RECIST 1.1.

9. Adequate organ function, including:

   • Hemoglobin ≥ 8 g/dL (blood transfusions are permitted)
   • Absolute neutrophil count ≥ 1000
   • Platelet count ≥ 100 x 10⁹/L
   • Glomerular filtration rate (GFR) ≥ 30 mL/min
   • Bilirubin ≤ 1.5 x ULN (upper limit of normal)

10. Written informed consent obtained from the patient.

11. At least 3 weeks must have elapsed from any prior therapy

Exclusion Criteria:

1. Uterine sarcoma
2. Active central nervous system metastases or leptomeningeal disease.
3. History of severe allergic reactions to pembrolizumab, lenvatinib, or any components of the formulations.
4. Active autoimmune disease requiring chronic systemic steroids for > 3 months in the last 6 months prior to enrollment.
5. Pregnancy or breastfeeding at the time of enrollment.
6. Previous treatment with lenvatinib or other VEGFR inhibitors.
7. Concurrent treatment with other investigational drugs or anti-cancer therapies except for adjuvant hormonal therapy for breast cancer.
8. Uncontrolled concurrent illness, such as active infections that could interfere with study participation.
9. Blood pressure >160 systolic or >110 diastolic averaged over last 3 documented measurements.
10. History of significant cardiovascular events within 12 months prior to enrollment, including myocardial infarction, unstable angina, or congestive heart failure (NYHA Class III or IV).
11. History of organ transplant or immune suppressive therapy that would interfere with the efficacy or safety of the investigational drugs.
12. Other malignancies within the past 2 years except for non-melanoma skin cancer.