MON-451 An Unusual Case of Follicular Thyroid Cancer with Pulmonary Metastasis and Concurrent Hyperthyroidism

Follicular Thyroid Cancer (FTC) accounts for approximately 12 % of all thyroid cancers and is the second most common cause of differentiated thyroid cancer. However, coexisting hyperthyroidism and thyroid malignancy is considered a rare event and is thought to have a prevalence of 0.21–9.0 %. We describe a compelling case of metastatic FTC initially presenting with subclinical hyperthyroidism progressing to overt hyperthyroidism. Clinical Case: An 88-year-old man with a history of prostate cancer, previous tobacco dependence, and hypertension initially presented with complaints of a chronic non-productive cough associated with unintentional weight loss and fatigue. Initial imaging included a chest CT that showed several bilateral pulmonary nodules suspicious for metastatic disease, as well as an enlarged left-sided thyroid mass, which extended from the inferior pole into the mediastinum. FDG PET/CT showed avid disease identified in the lung. CT-guided lung biopsy was performed, and histopathology revealed FTC. Thyroid function tests (TFTs) revealed a Tg level of 1427 (0.00–33.70), TgAb <1.0 (< 13.6), TSH 0.05 (0.40–4.50), FT4 1.1 (0.8–1.8) and FT3 3.4 (2.3–4.2). Biochemical testing was consistent with subclinical hyperthyroidism. Neck ultrasound showed bilateral thyroid nodules, the largest located on the left mid-pole measuring 3.4 x 3.2 x 3.7 cm. He underwent a whole-body I-131 diagnostic scan, which showed intense uptake of the radionuclide within the thyroid gland, more evident on the left, but additional metastatic lesions elsewhere in the visualized body were not possible. TFTs were repeated, which showed a TSH of 0.01, FT4 of 2.0, and FT3 of 6.4. He was subsequently started on methimazole daily and eventually became euthyroid. Due to advanced age, significant mediastinal extension, and lung metastasis, the patient was not a candidate for surgical resection and treatment with a targeted tyrosine kinase inhibitor. He ultimately opted for an observational approach. Conclusion: Although metastatic FTC carries a poor prognosis, concurrent hyperthyroidism is thought to be associated with a more aggressive disease course and higher mortality compared to differentiated thyroid cancers in euthyroid patients. Sources: 1. Pazaitou-Panayiotou, K., Perros, P., Boudina, M., Siardos, G., Drimonitis, A., Patakiouta, F., & Vainas, I. (2008). Mortality from thyroid cancer in patients with hyperthyroidism: the Theagenion Cancer Hospital experience, European Journal of Endocrinology, 159(6), 799–803. 2. Benjamin Momo Kadia, Christian Akem Dimala, Ndemazie Nkafu Bechem, Desmond Aroke. BMC Res Notes. 2016; 9: 369. 3. Parameswaran R, Shulin Hu J, Min En N, Tan WB, Yuan NK. Patterns of metastasis in follicular thyroid carcinoma and the difference between early and delayed presentation. Ann R Coll Surg Engl. 2017;99(2):151–154.