[Clinicopathologic characteristics of head and neck carcinoma showing thymus-like element].

To investigate clinicopathological features of carcinoma showing thymus-like elements (CASTLE) in the head and neck regions. Clinicopathological data of 7 patients with CASTLE in the head and neck regions were retrospectively reviewed.Immunohistochemical staining and in situ hybridization for EBER were performed. BRAF(V600E) mutation was examined by ARMS method in 6 cases. There were 5 females and 2 males with age between 49 and 78 years (average of 65.6 years). All tumors were solitary nodular lesions with an infiltrative border, including 6 intrathyroid tumors and 1 extrathyroid tumor in the laryngeal pharynx.The tumors were 1.7-4.1 cm in diameter (average of 3.0 cm). Four cases demonstrated lymph node metastasis.All patients were alive without metastasis during follow-up, except one consultation case (with FNA sample) developed recurrence at the primary site. The cases showed different immunoreaction to CD5, diffuse immunoreaction with p63, CK5/6 and CD117, but negative staining for TTF1, TG and calcitonin. One case showed positive immunoreaction with Synin less than 30% tumor cells. The Ki-67 labeling index was between 3% and 90%. No BRAF(V600E) mutation and EB virus infection were detected. Extrathyroid CASTLE involving laryngeal pharynx shows the similar morphological and immunohistochemical features with intrathyroid CASTLE.Immunohistochemical markers of CD5 and CD117 are helpful in the diagnosis. Ki-67 labeling index can be high in CASTLE, especially in lymphoepithelioma type. CD5-negative CASTLE may have neuroendocrine differentiation. BRAF(V600E) mutation and EB virus may not be involved in the carcinogenesis of CASTLE.