P-62 A CASE OF PAPILLARY THYROID CARCINOMA WITH ISOLATED BONE METASTASES
Authors: Akıncı Altundal Aslınur , Sakar Kenan , Gursoy Guven , Celik Serkan Yasar , Kupik Gulnihan Eren , Kupik Osman , Cullu Nesat , Akbaba Gulhan 
Published: January 2025

Abstract

Introduction
Thyroid carcinomas constitute less than 3% of all cancers (1). Papillary thyroid carcinoma (PTC) accounts for 80% of thyroid carcinomas and generally has a good prognosis(2). Lymph node metastases are frequently observed in thyroid cancers(30-40%). However, distant metastases are quite rare(1-4%)(2).

Clinical Case
A 52-year-old female patient presented to the neurosurgery department due to back pain of approximately 2 months. A mass lesion was observed in the T9 vertebral body on a thoracic CT scan, which was destroying the bone structure, causing a compression fracture in the vertebra, and extending into the spinal canal. A total laminectomy of T9 vertebra and partial laminectomies of T8 and T10 vertebrae were performed. Pathology revealed strongly positive for Vimentin, TTF-1, Thyroglobulin, and Pax 8, consistent with carcinoma metastasis. It was recommended to perform a whole-body scan, primarily focusing on the thyroid gland. PET-CT, thoracic and abdominal CT scans revealed a 62x48 mm metastatic lesion in the right iliac bone and metastatic involvement of the T9 vertebra, with no other pathological findings. The patient's history revealed that she had undergone a total thyroidectomy six years ago, and the result was reported as benign. She was on levothyroxine sodium replacement therapy. Blood tests revealed TSH: 0.288 (0.27-4.2 µIU/ml), T4: 18.7 (12-22 pmol/L), T3: 4.78 (3.1-6.8 pmol/L), Anti-Thyroglobulin Antibody: 60.8 (0-115 IU/ml), and Thyroglobulin: &gt;500 (3.5-77 ng/ml). Neck ultrasonography did not reveal any residual thyroid tissue or pathological lymph nodes. Given the suspicion of thyroid carcinoma metastasis and high thyroglobulin levels, the pathology preparations of the total thyroidectomy were re-consulted by our hospital's pathology department. The pathology result was consistent with papillary thyroid carcinoma composed of 55% follicular subtype and 45% solid/trabecular subtype. As surgery for the iliac bone metastasis was not considered appropriate, the patient was referred to the nuclear medicine department for radioactive iodine therapy and to the radiation oncology department for radiotherapy. The nuclear medicine, radiation oncology, and our department continue to follow up and treat the patient.

Conclusion
PTC is generally a slowly progressing cancer with a good prognosis. The most common site of metastasis in all PTC cases is the cervical lymph node, and only 3.5-3.8% have distant metastases(3). Distant metastases are most commonly seen in the lungs (53.4%), followed by bones (28.1%), liver (8.3%), and brain (4.7%) (1,4). Distant metastases significantly increase mortality from PTC. Therefore, the importance of adjuvant therapy (endocrine therapy, radiotherapy, etc.) and regular follow-up after thyroid cancer surgery should be emphasized. It should be kept in mind that, as in our case, papillary thyroid carcinomas can also present with isolated bone metastases without cervical lymph node metastases.