P-099 ANGIOSARCOMA OF THE THYROID GLAND DIAGNOSED AFTER THREE YEARS OF FOLLOW-UP: A DIAGNOSTIC CHALLENGE IN A 62-YEAR-OLD MALE

Abstract Introduction Thyroid angiosarcoma is an extremely rare and aggressive vascular tumor, with a higher incidence in regions with iodine deficiency. It is usually associated with rapid lymphatic and hematogeneous dissemination. Early diagnosis is difficult because of nonspecific clinical and cytological features, with the common diagnostic challenge being to distinguish it from an anaplastic thyroid carcinoma. Clinical Case A 62-year-old male was referred to the endocrinology clinic in 2022 after incidental finding of a large heterogeneous thyroid nodule (78 x 69 mm) with tracheal deviation and compression on thoracic computerized tomography (CT) during a COVID-19 (SARS-CoV-2) infection. Previous medical history was remarkable for well-controlled type 2 diabetes but negative for thyroid disease. Thyroid function tests showed a low-normal TSH (0.27 mIU/L) with normal free T4 and T3 concentrations. Serum thyroglobulin was elevated at 505 ng/ml, compatible with a voluminous goiter, and calcitonin was normal (7.5 ng/L). Calcium and phosphate were within normal limits. A fine needle aspiration biopsy (FNA) of the left thyroid nodule was compatible with cystic material resulting in a Bethesda Category I cytology. The patient was referred to surgery, which was postponed first due to patient preference and subsequently because of a myocardial infarction requiring dual antiplatelet therapy. In 2025, he underwent left lobo-isthmectomy. The surgery was complicated by intraoperative rupture of the capsule. Surprisingly, the surgical pathology showed a thyroid angiosarcoma without extrathyroidal extension. Immunohistochemistry was positive for CD31 and ERG, and negative for TTF-1, thyroglobulin and calcitonin. An 18-fluorodeoxyglucose (FDG)-positron emission tomography (PET-CT) 3 months post-surgery showed multiple suspicious cervical lesions and FNA confirmed the presence of locoregional metastases. Distant metastases were absent. Based on these findings, chemotherapy was initiated with doxorubicin and ifosfamide. A PET-CT after 2 cycles of chemotherapy showed an excellent partial response of the cervical lesions. Conclusion This case underscores the challenges in diagnosing thyroid angiosarcoma through FNA cytology. The false negative cytology result may have been caused by tumor heterogeneity and hemorrhagic cystic areas. Despite the delay in surgery, the clinical course was surprisingly indolent. The slow tumor progression in this case suggests that the clinical behavior of this rare entity, which is usually highly aggressive, can be heterogeneous. Early clinical suspicion and immunohistochemical markers (CD31, ERG) may be useful to facilitate the diagnosis. This observation also highlights that suspicious nodules require structured follow-up and surgical excision in the case of equivocal cytology results.