ESR1 and endometrioid adenocarcinoma: In summary, for endometrioid adenocarcinoma patients under 40 years of age with a strong desire to preserve fertility, endometrioid adenocarcinoma (type I), stage 1a, G1; MRI (preferred) or transvaginal ultrasonography showing lesions confined to the endometrium (normal CA125 level, pathologic diagnosis of highly to moderately differentiated and ER-positive, and tumors confined to the body of the uterus) and no extrauterine metastases, conservative treatment is feasible.