Ovarian high-grade follicular thyroid carcinoma with teratoma and NRAS mutation in an adolescent female: A case report.

Ovarian follicular thyroid cancer (OFTC) is a rare malignant struma ovarii that usually occurs in women aged between 30 and 50 years. The molecular pathogenesis and prognostic factors of OFTC remain poorly understood. Here, we present a case of a large cystic and solid mass in the left ovary of a 15-year-old female patient, who underwent single-port laparoscopic left adnexectomy. In addition to mature teratoma containing normal thyroid tissue, the tumor of thyroid cell origin had a nest-like or lamellar structure with intravascular thrombus, coagulation necrosis, and high mitotic image count, and lacked the nuclear features of papillary thyroid carcinoma. Immunohistochemical markers were positive for PAX-8, TTF-1 and TG. The final diagnosis was high-grade OFTC with teratoma. NRAS (Q61R) mutations were detected by whole exome sequencing and fluorescence quantitative PCR in OFTC samples, indicating that the pathogenesis of the tumor resembled that of follicular carcinoma of the thyroid. The occurrence of OFTC in adolescent females is very rare. High-grade OFTC is classified based on primary thyroid cancer, and its assessment in ovarian tumors has not been reported. Further research is required to elucidate its molecular mechanisms and prognostic factors through the accumulation of more cases.