12570 Papillary Thyroid Carcinoma Found In A Malignant Struma Ovarii

Abstract Disclosure: A. Arunachalam: None. P. Iyer: None. Struma ovarii is a monodermal teratoma primarily composed of mature thyroid tissue.[1] Depending on histologic findings, struma ovarii can be classified as benign or malignant. Among malignant struma ovarii, papillary type is the most common.2Women with struma ovarii can present with pelvic pain and less frequently ascites. Clinical features of hyperthyroidism can occur.[3] We present a 66 year old female of Chinese descent status post hysterectomy and left oophorectomy in 9/2021, prior right oophorectomy in 1985 with pathology consistent with a teratoma as per patient, who presented after being lost to follow-up. Her pathology of her left ovary showed diffuse thyroid tissue with focal areas consistent with papillary thyroid carcinoma. Her initial diagnosis was found in the setting of abdominal pain. She had a transvaginal ultrasound with a 16.9 x 13.1 x 8.9 cm cystic mass. Patient was lost to follow-up .She denied any symptoms of hyper or hypothyroidism. On biochemical evaluation, TSH 1.45 mcunit/ml, FT4 0.91 ng/dl, Thyroblobulin 4.21 ng/ml, Thyroglobulin Antibody undetectable. Thyroid ultrasound was significant for a 0.5 left thyroid isthmus nodule which was benign after FNA biopsy. CT chest, abdomen, pelvis without any evidence of distant metastasis. Decision was made to monitor with repeat thyroid ultrasound and biochemical evaluation in one year because no evidence of concerning lesions in the thyroid for PTC or evidence of distant metastasis. The frequency of struma ovarii among ovarian teratomas is less than 3% which makes this case rare. The most common sites of metastasis of a malignant struma ovarii include abdominal cavity, liver, lungs, brain and bone.[4] In certain cases, thyroid tissue found in struma ovarii can secrete T3 and T4.[5] Our patient had no abnormalities on imaging of the thyroid with normal thyroid function tests. We recommended monitoring of the thyroid gland to assess for malignant transformation. Mainstay of treatment is hysterectomy and bilateral salpingo-oophorectomy for postmenopausal women and unilateral salpingo-oophorectomy or cystectomy for women in the reproductive age. For metastatic struma ovarii, thyroidectomy and adjuvant treatment with radioactive iodine can be considered.[6]The risk of recurrence is lower based on size, location and histopathological features of the tumor. One study proprosed following unilateral salipingo-oophorectomy in patients with low risk of recurrence, TSH suppression at 0.1 to 0.5 mIU/L..[7] Considering the findings for our patient who presents years after hysterectomy and left oophorectomy in 2021 with normal thyroid gland on ultrasound and appropriate thyroid function tests, we recommended no additional complementary treatment with monitoring of labs and imaging in one year. This patient currently shows no evidence of metastatic disease or high risk of recurrence but long term monitoring remains a mainstay of the management. Presentation: 6/2/2024