MON-786 Malignant Struma Ovarii With Papillary Thyroid Carcinoma: A Case Report

Abstract A. Bassatne: None. M. Paravastu: None. A.P. Calimag: None. T. Yasmeen: None. Background: Struma ovarii is a rare monodermal ovarian teratoma that consists predominantly of thyroid tissue. It accounts for 1% of all ovarian tumors. It is mostly benign but malignancy consisting of papillary or follicular carcinoma have been reported in 5-10% of cases. It often presents with non-specific symptoms, leading to misdiagnosis or delays in the initiation of appropriate treatment. We report a rare case of a patient with non-specific abdominal pain who was diagnosed with struma ovarii with ectopic papillary thyroid cancer and biochemical hyperthyroidism. Case: A 32 y/o woman with no PMH presented to the ED for evaluation of RLQ abdominal pain with associated nausea for one week. CT scan of the abdomen/pelvis revealed a large enhancing mass in the right lower abdomen with inability to exclude malignancy. MRI pelvis confirmed a 10.8 x 10.1 x 8.3 cm heterogenous enhancing mass in the right ovary suspicious for neoplasm. There was a second 7.2 cm mass in the left ovary consistent with a dermoid cyst. She was discharged with pain control and scheduled for outpatient follow up with Gynecology. The patient presented to the ED again two days later with persistent RLQ abdominal pain. She was evaluated by gynecology who completed a serologic workup including bHCG, CA125, CEA, CA19-9, AFB, inhibin A/B, and LDH. Laboratory workup was negative except for a mildly elevated CA 19-9. She underwent bilateral ovarian cystectomy, right salpingo-oophorectomy and omentectomy. The final pathology confirmed a monodermal teratoma with focal (1cm) transformation to papillary thyroid carcinoma in the right ovary and a mature cystic teratoma in the left ovary. TSH was low at 0.018 mcU/ml (Ref range 0.35-5.00 mcU/ml), FT3 and FT4 were within a normal range. The patient did not endorse any symptoms of hyperthyroidism. The omentum and pelvic washing were negative. Next Generation Sequencing for papillary thyroid cancer biomarkers were not detected. Repeat TSH, free T4, thyroglobulin, and TSI levels were all within a normal range. The patient is currently scheduled to undergo a PET scan and thyroid ultrasound. She may need to undergo further treatment with total thyroidectomy and/or radioactive iodine (RAI) based on imaging results. Discussion: Struma ovarii can present with non-specific abdominal symptoms. Although rare, physicians should have a high suspicion for this diagnosis when an ovarian mass is discovered. It is crucial to test for hyperthyroidism prior to resection to prevent thyroid storm. Due to its rare occurrence, guidelines for treatment are not available. Surgical resection can range from cystectomy to total hysterectomy and oophorectomy. Subsequent treatment includes TSH suppression, RAI or total thyroidectomy. The choice of treatment should be individualized based on tumor characteristics such as size, presence of metastasis, and patient wishes including plans for future pregnancies. Monday, June 3, 2024