Hurthle Cells Adenoma With Distant Metastases Refractory to Radioiodine

Introduction: Adenoma of the thyroid is defined as an encapsulated follicular tumor that is well delimited in relation to the adjacent parenchyma and whose cells do not exhibit the nuclear alterations of papillary thyroid carcinoma (PTC), and in the absence of capsular and vascular invasion. Adenoma, including the of Hurthle cells, is considered a benign tumor. No additional treatment is recommended after resection of the tumor. Case: A 64-year-old man was submitted to total thyroidectomy because of a nodule measuring 3.5 cm with indeterminate cytology (predominance of Hurthle cells). Histology revealed an Hurthle cells adenoma of 3.2 cm. The tumor did not exhibit vascular or capsular invasion, the cells did not contain nuclei of PTC, and no necrosis or mitoses were observed. Five years after surgery, serum thyroglobulin (Tg) was elevated (25 ng/ml) during euthyroidism (TSH 0.6 mUI/l) and in the absence of anti-Tg antibodies. Serum calcitonin was undetectable. The patient developed a progressive increase in Tg and neck ultrasonography (US), chest computed tomography (CT), and FDG-PET/CT were performed. US revealed atypical lymph nodes (the largest with 12 mm) and cytology showed abundance of Hurthle cells. Chest CT detected multiple nodules, the largest measuring 15 mm, and FDG-PET/CT revealed areas of cervical and pulmonary uptake corresponding to the lesions seen on US and CT. The patient received 100 mCi radioactive iodine and post-therapy whole-body scanning showed mild uptake only in the thyroid bed. The patient continues to show progressive increase in Tg (last measurement > 1,000 ng/ml), as well as progression of metastases. He remains under follow-up and on therapy with tyrosine kinase inhibitor. The histology result was revised by two pathologists with broad experience in thyroid pathology who confirmed the initial findings compatible with adenoma. Conclusion: The present case shows that, although rare, Huthle cells tumors can develop metastases even when the tumor is < 4 cm and unequivocally without nuclei of PTC or capsular and vascular invasion, thus considered benign (adenoma). As observed in this case, these metastases can be macrometastases, distant, and refractory to radioiodine. Reference: Lloyd RV, Osamura RY, Klöppel G, Rosai J, ed. WHO Classification of Tumours of Endocrine Organs. 4(th) edition Lyon: IARC; 2017