Abstract #1397957: Papillary Thyroid Carcinoma Arising from Malignant Struma Ovarii

Abstract

Struma ovarii is a rare ovarian teratoma characterized by the presence of thyroid tissue. It can be functional leading to hyperthyroidism or transform into malignant thyroid cancer. We present a case of a 46-year-old woman without risk factors for thyroid cancer, who was found to have a cystic ovarian lesion suspicious for malignancy. Surgery revealed struma ovarii with papillary thyroid cancer. A 46-year-old woman presented with right lower quadrant abdominal pain associated with urinary incontinence. She was found to have palpable mass in the lower abdomen on physical examination. Abdominal/pelvic computed tomography (CT) scan showed a 12.7 cm right ovarian complex cystic lesion and a 5.9 cm left ovarian complex cyst. She underwent total abdominal hysterectomy, bilateral salpingo-oophorectomy, radical pelvic dissection, and omental biopsy. Pathology revealed struma ovarii of the right adnexa, with a 1.8 cm papillary thyroid cancer noted to be well to moderately differentiated without ovarian surface or fallopian tube involvement. It was staged as pT1aNxMx. BRAF mutation was negative. The contralateral ovary, fallopian tubes, and uterus were negative for malignancy. Post-operative labs included thyroglobulin antigen of 20.1 ng/ml, thyroglobulin antibodies were undetectable, thyroid stimulating hormone (TSH) of 3.53 mIU/L (0.4-4.5 mIU/L) and Free T4 of 1.1 ng/dl (0.8-1.8 ng/dl). Thyroid ultrasound (US) showed a 6 mm hypoechoic nodular lesion in the right isthmus. She was started on levothyroxine to suppress her TSH to the low normal level and she is planned to follow up on the small thyroid nodule with US in 3-5 years. The vast majority of struma ovarii are benign in nature and less likely to transform into malignant tissue. Most of the tumor transformation occurs in the form of papillary thyroid carcinoma, and the risk tends to be higher with larger-size ovarian teratomas >5 cm. The presenting symptoms are indistinguishable between benign and malignant tumors, and usually present with lower abdominal pain. Diagnosing papillary thyroid cancer in struma ovarii tumors is often challenging given the lack of distinct imaging characteristics and specific tumor markers. Additionally, cancer antigen 125 (CA-125) has no value. The mainstay for management is surgical resection. Regardless of the surgical strategy used, patients with malignant struma ovarii have an excellent disease-specific survival rate overall. However, staging is key to assessing if thyroidectomy and radioactive iodine are needed. Surveillance with thyroid imaging and biochemical markers is recommended, however, the disease is curable in most cases.