SUN-481 A Coexisting Primary Papillary Thyroid Carcinoma in a Case of Malignant Struma Ovarii with Follicular Thyroid Carcinoma: 2 Types of Thyroid Cancer in the Same Patient

Introduction: Struma ovarii is a rare monodermal variant of ovarian teratoma diagnosed when thyroid tissue is more than 50% of the overall tissue. It represents only 1% of all ovarian tumors. The vast majority of struma ovarii are benign (95%); however, malignant tumors have been reported in a small percentage of cases. The most common type is papillary carcinoma(PTC), followed by typical follicular carcinoma found in the pathology after surgical oophorectomy. We report a case of malignant struma ovarii with follicular carcinoma in the setting of additional micro PTC found after total thyroidectomy. Case report: A 48-year-old female presented with right-sided pelvic pain and a mobile pelvic mass. Pelvic MRI showed noted a large complex solid mass with cystic components in the right adnexa. It measured 7.7 x 8.4 x 6.7 cm. Subsequently, the patient underwent a robotic hysterectomy, bilateral salpingo-oophorectomy (TAHBSO), bilateral pelvic and para-aortic lymph node sampling, omentectomy and resection of nodules. Final pathology noted an ovary with struma ovarii with well-differentiated follicular carcinoma, peritoneal nodules containing thyroid tissue and benign lymph nodes. Subsequently, iodine 123 SPECT CT showed physiologic uptake in the thyroid with increased uptake in the pelvis, right perirectal region indicating residual thyroid tissue. The patient underwent total thyroidectomy with radioactive ablation with I131 (154.7 mCi). Pathology detected incidental 0.5mm micro PTC and it was classified as staged pT1aN. 6 months postoperatively, thyroglobulin (Tg) and Tg antibodies were undetectable with no abnormalities found on repeat whole-body scans. The patient has been following up with no new issues for the past 5 years indicating a good prognosis with low risk of recurrence. Discussion and Conclusion: In the literature, Struma ovarii containing thyroid-type carcinoma and papillary or follicular thyroid carcinoma metastasizing to the ovary has been documented. The standard treatment of a patient with malignant struma ovarii is TAHBSO and complete surgical staging, including peritoneal washings for cytology, pelvic and para-aortic lymph node sampling, and omentectomy. In cases with the residual malignant disease after surgery, total thyroidectomy and radioactive ablation are recommended. Our case is a unique case given the presence of 2 different thyroid carcinoma in the same patient. In addition, our patient had multiple risk factors for recurrence including large lesions>4 cm, extra ovarian extension, and the coexisting synchronous primary thyroid cancer, however, she had a good prognosis with no recurrence during the 5 years follow up period.