Endocrine Abstracts

Introduction: Follicular thyroid carcinoma (FTC) is the second most common malignancy of the thyroid gland. Distant metastasis, usually in bones or lungs, can be found in about 10%–15% of cases. A clinical case of FTC distant bone metastasis is presented.

Case: A 62-year-old male came to endocrinologist for annual follow-up (FU) of multinodular goiter, euthyreosis in 2010. Two years before prostate carcinoma (T1N0M0) was also diagnosed for the patient and brachytherapy was adjusted. At that time small pelvis computed tomography (CT) scan showed a focal lesion with cortical bone destruction in the upper ramus of the right pubic bone. Management and outcomes: thyroid ultrasound scan (US) showed nodes in both thyroid lobes up to 23 mm of diameter. After fine needle aspiration (FNA) only benign follicular epithelium changes were found. Blood test showed normal thyroid-stimulating hormone (TSH) 0.71 mU/l, but highly elevated thyroglobulin (Tg) 2030 mcg/l. In 2011 Tg increased (4920 mcg/l), during thyroid US nodes with calcifications were diagnosed, therefore FNA was performed and benign follicular epithelium changes were found again. After 6 months blood tests were performed: Tg 6888 mcg/l, TSH, TPOAb and TgAb were within the normal range, FNA was repeated for the third time and follicular epithelium proliferation was found. Total thyroidectomy was recommended, but surgeon refused it. Thyroid US showed no significant changes during FU period, but Tg was markedly elevated (>30,000 μg/l). In 2014 the patient had a pubic bone fracture and bone biopsy revealed metastasis of follicular thyroid carcinoma (TTF-1: 100% tumor cells had strongly positive nuclear staining; Tg: 90% tumor cells had strongly positive cytoplasmic staining). Total thyroidectomy was performed in 2014, the histology showed benign thyroid hyperplasia with no signs of follicular carcinoma. SPECT and low dose CT scan of pelvis was performed after 1 month and radioactive iodine-131 (I-131) accumulation was found in the thyroid bed and intensive accumulation on the right side of pelvis (around 75×65 mm lesion). I-131 therapy was indicated and cumulative 28,8 GBq dose was adjusted since 2014. The patient is still followed-up and Tg levels after I-131 were decreasing for 3 years till 56.9 μg/l, unfortunately in 2018 Tg levels increased (1345 mcg/l) and primary tumor is still not found.

Conclusion: This case is exceptional because of its rarity and also due to the incapability to find the primary tumor.