A 63-year-old man presented with a tumor localized on the right side of the neck which has gradually enlarged during the last 2 years. Computed tomography (CT) revealed a 76 mm solid mass in the right lobe of the thyroid gland, displacing the trachea medially, common carotid artery posteriorly, and sternocleidomastoid muscle laterally. The lesion had heterogeneous contrast enhancement with lobulated contour, and internal macrocalcifications with necrotic areas were obvious [Figure 1]. There were metastatic lymph nodes in cervical lymph node stations of 2-3-4-5 and the supraclavicular region. Thoracic CT showed mediastinal lymph nodes and lung metastases.
The FNA was hypercellular not only as single cells but also insular and trabecular arrangements were noticed [Figures 2 and 3]. Colloid was scarce and necrosis with accompanying polymorphonuclear leukocytes was seen in the background. Cells were uniform and had large granular cytoplasm with an increased nuclear/cytoplasmic ratio. Nuclei were round, slightly hyperchromatic, and macronucleoli were prominent [Figure 4]. Nuclear pleomorphism was not striking. Except for nuclear membrane irregularity as rasinoid, the rest of the characteristic nuclear features of papillary thyroid carcinoma and medullary thyroid carcinoma were absent.
Immunohistochemical analyses were performed on the cell-block [Figure 5]. TTF-1 and PAX-8 revealed diffuse nuclear positivity, whereas p53 was positive in 9.2% of cell nuclei [Figures 6 and 7]. Pan-CK showed extensive and thyroglobulin (TG) weak focal cytoplasmic staining. Ki-67 proliferation index was 10%. Carcinoembryonic antigen (CEA), calcitonin, and Bcl-2 were negative. All immunostains were correlated with convenient positive controls.
Based on the monomorphic oncocytic morphology, the presence of necrosis, immunohistochemical profile, and clinicoradiologic findings; FNA diagnosis was given as "malignant; highly suggesting oncocytic variant of poorly differentiated thyroid carcinoma" according to TBSRTC. The patient was considered inoperable due to the radiologic findings and received chemo/radiotherapy. No further metastases were detected with positron emission tomography in the clinical follow-up of 18 months.