Carcinoma showing thymus-like differentiation (CASTLE) with neuroendocrine differentiation.

Carcinoma showing thymus-like differentiation (CASTLE) is a rare malignant neoplasm that histologically resembles thymic carcinoma and arises in the thyroid gland or adjacent soft tissue of the neck. Herein is reported the case of a 62-year-old male patient with CASTLE exhibiting neuroendocrine differentiation, who was treated with total pharyngolaryngo-esophagectomy and total thyroidectomy. Gross examination of the surgical specimen showed a grayish-white, solid, lobulated tumor, mainly located between the trachea and esophagus, and involving the lower part of the left thyroid lobe. Histologically, the tumor consisted of epithelial cell nests separated by thick fibrous septa. The tumor cells were polygonal in shape, and contained pale cytoplasm and a vesicular nucleus with prominent nucleoli. There were few mitotic figures. Rosette-like arrangements that suggested neuroendocrine differentiation were observed in part of the tumor. The tumor cells were positive for CD5 and neuroendocrine markers including synaptophysin and chromogranin A.