Endometriotic cyst mimicking recurrence after treatment for ovarian immature teratoma: a case report

Background Endometriosis is common in reproductive-age women, but the development of an endometriotic cyst that mimics tumor recurrence during follow-up after treatment for ovarian immature teratoma poses a significant diagnostic challenge, particularly for young patients requiring fertility preservation. Case presentation A 23-year-old woman with a history of two fertility-sparing surgeries and BEP (bleomycin, etoposide, cisplatin) chemotherapy for ovarian immature teratoma was followed up. Pelvic MRI revealed a 5.7×4.5cm left adnexal multicystic lesion, suggestive of hemorrhagic content, and without restricted diffusion. Tumor markers (CA125, CA199, AFP, CEA) remained within normal limits. Although a clinical diagnosis of endometriotic cyst was considered, the possibility of recurrence could not be completely ruled out. Given the high risk of irreversible ovarian damage from a third surgery and the patient’s refusal of needle biopsy, a trial of gonadotropin-releasing hormone agonist (GnRH-a) therapy was initiated. After three cycles, the mass markedly decreased to 1.4 × 0.9 cm. Maintenance dienogest was subsequently given. At one-year follow-up, there was no evidence of disease progression; the patient maintained regular menstrual cycles and ovarian reserve was preserved (anti-Müllerian hormone (AMH) >2ng/mL), supporting a clinical diagnosis consistent with an endometriotic cyst. Conclusion This case suggests that, in carefully selected patients with reassuring clinical, imaging, and laboratory findings and under close oncologic surveillance, a therapeutic trial of hormonal therapy may serve as an alternative to immediate surgical exploration for a newly developed adnexal mass after treatment for malignant ovarian tumors, especially when fertility preservation is a priority.