Case Report: Ovarian endometrioid tumor occurring in a patient with early-stage, low-risk endometrial carcinoma successfully treated by fertility-sparing management

Rationale Endometrial carcinoma (EC) increasingly affects younger women, prompting interest in fertility-sparing treatments. Although hormonal therapy is a feasible option for carefully selected patients, there remains a substantial risk of recurrence or associated ovarian malignancy. Case presentation A 35-year-old premenopausal woman reported abnormal uterine bleeding characterized by increased menstrual flow over approximately one year. Diagnosis and intervention She was diagnosed with stage IA, grade 1 EC managed initially with high-dose oral megestrol acetate followed by a levonorgestrel-releasing intrauterine system due to intolerance. Serial endometrial biopsies demonstrated histologic remission, after which the patient elected definitive surgery with hysterectomy and bilateral salpingectomy while preserving the ovaries. Uterine pathology confirmed absence of residual carcinoma. Follow-up and outcomes During follow-up, a right adnexal cystic-solid mass was detected and categorized as Ovarian-Adnexal Reporting and Data System (O-RADS) ultrasound category 4, with MRI features raising suspicion. Comprehensive surgical staging confirmed a unilateral low-grade ovarian endometrioid carcinoma with squamous differentiation; staging and peritoneal cytology were negative. The patient recovered uneventfully and remains under surveillance without adjuvant therapy. Lessons This case highlights the rare occurrence of metachronous ovarian endometrioid carcinoma after successful fertility-sparing and hysterectomy, underscores the importance of shared decision-making regarding ovarian preservation, and supports risk-adapted surveillance strategies in this population.