Cytokeratin7 expression in histologic and cytologic specimens of cystic neck metastasis from HPV positive squamous cell carcinoma of the tonsil: A case report

The majority of cystic squamous cell carcinomas (SCCs) of the neck have been shown to be metastatic tumors from tonsillar SCCs associated with high‐risk human papillomavirus (HR HPV). Recent studies have demonstrated cytokeratin (CK)7 involvement in the development of HPV positive SCC, but no report has been issued on its simultaneous expression in primary tonsillar and metastatic tumor with cystic change. We present a case of HPV positive tonsillar SCC of a 42‐year‐old male that initially manifested as a cystic neck mass expressing CK7, CK19, and p16 in primary and metastatic tumors. Immunohistochemical examination revealed diffuse CK19 and p16 expression, and patchy CK7 expression in the solid components of primary and metastatic tumors. However, in cystic components of metastatic tumors the expression of CK7 and CK19 was preserved but p16 expression was absent, which was consistent with immunocytochemical findings of fine‐needle aspirates from cystic neck mass. In immunocytochemistry performed on aspirates of a branchial cleft cyst for the comparison of cystic SCC and benign cyst, CK19 staining was positive but CK7 and p16 staining was negative. These results suggest that CK7 immunocytochemistry on aspirated material from cystic neck mass may be a useful adjunct for distinguishing cystic metastasis of tonsillar SCC from branchial cleft cyst, although a larger scale study would be required.