Recurrent Immature Teratoma Mimicking Growing Teratoma Syndrome Following Initial Resection: A Diagnostic Pitfall

Background Growing teratoma syndrome (GTS) is a rare condition characterized by the enlargement of metastatic masses during or after chemotherapy for malignant germ cell tumors (GCTs), despite normalized tumor marker levels. It is defined by three criteria: (1) enlarging or new masses during or after chemotherapy, (2) normal tumor marker levels, and (3) histological presence of only mature teratoma elements. Differentiating GTS from recurrent immature teratoma is challenging, as both conditions may present similarly in imaging and tumor marker profiles. Case Presentation We report the case of a 20‐year‐old woman diagnosed with a mixed ovarian GCT, consisting of grade 2 immature teratoma and yolk sac tumor. After undergoing right salpingo‐oophorectomy and chemotherapy, she remained in remission for 4 years. Follow‐up imaging revealed enlarged para‐aortic lymph nodes. Due to normal tumor markers and a lack of response to chemotherapy, the condition was initially diagnosed as GTS, prompting surgical resection of the lymph nodes. Histopathological analysis, however, revealed immature neuroepithelial elements consistent with grade 3 immature teratoma, contradicting the GTS diagnosis. The final diagnosis was revised to recurrent immature teratoma. Conclusion This case highlights the diagnostic challenges in distinguishing between GTS and recurrent immature teratoma. While normal tumor markers and tumor growth following chemotherapy may suggest GTS, histopathological confirmation is essential. Clinicians should maintain a high index of suspicion for recurrent immature teratoma in cases mimicking GTS and consider surgical resection for definitive diagnosis. Multidisciplinary evaluation remains crucial in the management of ovarian GCTs.