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

Objective: To investigate clinicopathological features of carcinoma showing thymus-like elements (CASTLE) in the head and neck regions. Methods: 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. Results: 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. Conclusions: 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.