Based on the above situation, the investigators propose the following scientific hypothesis: In young patients with early MMRd type EC, the use of immune checkpoint inhibitors combined with progesterone for fertility retention therapy can improve the therapeutic efficacy, reduce recurrence, and improve tumor prognosis. Based on the above assumptions, this project intends to conduct a prospective exploratory clinical study in EC patients limited to the endometrial layer or superficial myometrium (FIGO 2023 IA1-IA2 stage). The subjects were treated with TQB2450 periodic intravenous drip + high-potency progesterone daily oral therapy. During the treatment period, hysteroscopy was performed every 12 weeks to evaluate the therapeutic efficacy. The primary endpoint was the 12-week CR rate; the secondary endpoints included the 24-week CR rate, the 36-week CR rate, the median CR time, the 1-year relapse rate, the 2-year relapse rate, the median relapse time, the pregnancy rate, the live birth rate, and drug-related adverse reactions. The exploratory indicators were the response of different MMRd tumors to immune checkpoint inhibitors and their possible mechanisms. The development of this study will provide a clinical basis for improving the fertility-preserving treatment regimen of MMRd EC.