Inclusion Criteria:
1. Aged 18-75 years.
2. Histopathologically confirmed endometrial cancer, with pathological types including endometrioid, serous, clear cell, undifferentiated, dedifferentiated, or carcinosarcoma.
3. Laboratory-confirmed dMMR (mismatch repair deficient) endometrial cancer (loss of MLH1/PMS2/MSH2/MSH6 protein expression by immunohistochemistry) or MSI-H (microsatellite instability-high by PCR or NGS).
4. Stage I-II according to the FIGO 2023 staging system.
5. At least one measurable lesion (RECIST 1.1 criteria).
6. ECOG performance status 0-1, with a life expectancy of ≥12 months.
7. Strong desire for uterine preservation, conservative treatment, or fertility preservation, or inability to tolerate standard surgery due to comorbidities.
8. Adequate organ function within 14 days prior to enrollment.
9. Good follow-up conditions and signed informed consent.
Exclusion Criteria:
1. Presence of active autoimmune disease, or long-term requirement for immunosuppressive agents;
2. Prior treatment with immune checkpoint inhibitors;
3. Concurrent persistent or active infections, such as hepatitis B, hepatitis C, etc.;
4. Concurrent severe dysfunction of vital organs including heart, lung, liver and kidney: alanine aminotransferase/aspartate aminotransferase elevated more than 3 times the upper limit of normal (ULN) and unresponsive to liver-protective therapy; serum creatinine ≥1.5 × ULN; abnormal thyroid function; history of heart failure, unstable angina pectoris, severe arrhythmia, myocarditis, interstitial lung disease, non-infectious pneumonitis or active pulmonary infection, etc.;
5. Other active malignant tumors (except cured basal cell carcinoma of the skin, cervical carcinoma in situ, etc.);
6. Known hypersensitivity to any component of the study drug;
7. Pregnant or breastfeeding women;
8. Any severe or unstable concomitant disease that, in the investigator's judgment, renders the subject ineligible for this study.
