A 34-year-old woman presented with a 2-month history of sore throat. The patient had no notable medical or family history. Physical examination revealed a palpable right thyroid mass. Thyroid function and calcium tests were within normal limits. Ultrasound showed a 1.7-cm, well demarcated, heterogeneous, low echoic solid mass in the lower pole of the right thyroid (). A computed tomography scan of the neck revealed a 3.3-cm, exophytic, low-attenuated mass in the lower pole of the right thyroid. The FNA biopsy of the mass was performed, which was accompanied by the standard Papanicolaou stain.\nThe smear was composed of not only cohesive three dimensional clusters and sheets but also singly scattered cells (). The tumor cells showed mild anisonucleosis and high nuclear : cytoplasmic (N/C) ratios. Nuclei were round to ovoid with irregular nuclear contours and small, distinct nucleoli (). The nuclear chromatin was vesicular or coarsely granular. Nuclear grooves were rarely seen. Cytoplasm was scanty and amphophilic. Cytoplasmic border was indistinct. Some tumor cells showed dense orangeophilic cytoplasm, which is suggestive of individual cell keratinization (). Some lymphocytes were found on the background and within clusters, which was accompanied by the presence of a few stripped nuclei (). Mitotic figures were rarely seen. Intranuclear cytoplasmic inclusions were not observed. Papillary or follicular structure was not observed. The aspirate was interpreted as a high-grade malignant thyroid neoplasm without further definitive classification. The total thyroidectomy was performed.\nOn gross examination, the thyroid contained a 4.0-cm solid mass replacing most of the right thyroid. The mass had a lobular, tan-colored cut surface and a firm consistency (). On microscopic examination, the tumor was well-circumscribed and it was composed of variably sized and irregularly shaped lobules of cohesive polygonal tumor cells which were separated by bands of dense fibrous stroma (). The tumor cells had high N/C ratios, eosinophilic cytoplasm and ill-defined cell borders. The nuclei were vesicular or coarsely granular with prominent nucleoli. The mitotic figures were sparse. There was mild lymphoplasmacytic infiltration within the tumor nodules and septae. Cytoplasmic keratinization was seen. The tumor cells showed positivity for CD5, carcinoembryonic antigen, high molecular weight keratin (HMWK), cytokeratin 5 (CK5), and p63. The tumor was negative for thyroid transcription factor-1, thyroglobulin, and calcitonin. Vascular invasion and extensive extra-thyroidal extension were present. One regional lymph node was found and involved by tumor.\nOver a 27-month follow-up period, the patient had no evidence of tumor recurrence.
The patient, a 28-year-old man with a 3-month-old mass in the neck was referred to our department. The mass, located on the left thyroid lobe, was elastic, hard, showed limited mobility, and measured approximately 30 × 20 mm. There was no remarkable tenderness over the mass.\nBlood examination results were normal, including levels of thyroid-stimulating hormone, free thyroid hormone, and thyroglobulin (Table ). Ultrasonography revealed a hypoechoic solid mass in the lower pole of the left thyroid lobe with a poorly marginated heterogeneous pattern (Fig. ). Computed tomography revealed a heterogenic tumor in the left thyroid lobe (Fig. ). 18F-fluorodeoxyglucose (18F-FDG) accumulated in the thyroid tumor on positron-emission tomography. The standardized uptake value of 18F-FDG was 5.29 (Fig. ). Fine-needle aspiration cytology (FNAC) showed a number of lymphoid cells without atypia that were similar to those seen in malignant lymphoma of the thyroid (Fig. ).\nAs we diagnosed a highly malignant thyroid cancer (cT2N0M0), we performed a left hemithyroidectomy with central neck dissection (ND). Histopathological findings showed that the tumor was composed of irregular insular nests of neoplastic cells and had an expansive growth pattern in the thyroid (Fig. ). The carcinoma cells had round nuclei or polymorphonuclei with well-defined nucleoli and ill-defined cell borders (Fig. ). Immunohistochemical studies showed that the tumor was partially positive for CD5, positive for Ki-67 (approx. 30%), and negative for CD20, calcitonin, and thyroglobulin (Fig. ). Based on these histopathological findings, the tumor was finally diagnosed as CASTLE. There were no signs of recurrence without additional treatment after 10 years of follow-up.