A Rare Urothelial Malignant Transformation in a Mature Cystic Teratoma of the Ovary.

Approximately 0.17-2% of mature cystic teratomas undergo malignant transformation, of which squamous cell carcinoma (SCC) is the most common, accounting for 80% of these cases. Urothelial malignant transformation is extremely rare. The present study involves a 58-year-old patient who visited the hospital with discomfort in the lower abdomen. USG and pelvic MRI showed a left ovarian mature cystic teratoma. Left salpingo-oophorectomy was performed, and pathological examination revealed urothelial carcinoma transformation of the mature cystic teratoma morphologically and immunohistochemically. No metastasis to other organs was identified by CT after the surgery. Additional surgery, including total hysterectomy, right salpingo-oophorectomy, omentectomy, and dissection of pelvic and para-aortic lymph nodes, was performed without complications. No tumors were identified elsewhere, and the patient's stage was confirmed as IA. She had an uneventful postoperative course and was discharged 10 days later. CT showed no metastasis or recurrence six months later.