PSAT287 Metastatic Thyroid Carcinoma from an Old Teratoma

INTRODUCTION: Struma ovarii is rare and makes up 1% of all ovarian tumors out of which only 5-10% are malignant. We present the third reported case of delayed bony metastasis of malignant struma ovarii years after surgical removal. CLINICAL CASE: A 63 years old female with a medical history of cerebral palsy and teratoma resected in 2013, presented with complaints of right arm pain for 6 months in 2019. Routine lab work and X-rays of the right humerus were normal. An arthrogram showed a destructive process involving the proximal humeral meta-diaphysis, presumably malignant in etiology which was confirmed by a CT scan of the upper arm. A PET scan subsequently showed increased tracer activity associated with the right humeral head and neck along with replacement of marrow cavity by soft tissue density material. A fine needle aspiration of the lesion showed metastatic carcinoma of thyroid follicular origin. Serum TSH was 2.369 miu/ml (normal 0.350-5.500 miu/ml). An ultrasound of the neck demonstrated a normal thyroid without any identifiable nodules. She underwent radical resection of the right proximal humerus with endo-prosthetic reconstruction followed by postoperative radiation to the right shoulder. A repeat bone scan 3 months later showed increased activity in the ribs bilaterally and the distal right humerus. This was followed by a total thyroidectomy that showed no evidence of follicular cancer. A repeat TSH 8 weeks later came back at 88.36miu/ml but surprisingly even after the removal of thyroid gland the serum thyroglobulin remained elevated at 62.2 ng/ml (normal 2.8-40.9 ng/ml). This prompted a nuclear medicine thyroid whole body scan which revealed metastatic disease to the lumbar spine and multiple metastases to the abdomen. Treatment with radioactive iodine was started. The treatment, however was considered suboptimal in her case and she was started on radiation therapy which she is still receiving. DISCUSSION: Struma ovarii is a specialized ovarian teratoma made up of more than 50% mature thyroid tissue. Of these only 5-10% have malignant potential with less than 200 cases ever being reported. The NRAS, BRAF and JAK3 oncogene mutations have been implicated in the pathogenesis but the exact cause is unknown, resulting in the absence of any guideline directed therapy. The most common sites of metastasis are the peritoneum, mesentery and omentum. Bones are a less common metastatic site. Current treatment strategies include total thyroidectomy with iodine ablation and radioiodine scanning with serum thyroglobulin levels being followed as a tumor marker. It can rarely present as a late metastatic disease years after surgical resection of the tumor and a high index of suspicion is required to make the correct diagnosis. Presentation: Saturday, June 11, 2022 1:00 p.m. - 3:00 p.m.