Cytokeratin 5 & 6 (D5 & 16B4)

Anti-CK 5 & 6 positivity is seen in 65% to 100% of epithelioid mesotheliomas, in 0% to 19% of lung adenocarcinomas, and in 22% to 80% of serous carcinoma of the ovary and peritoneum.1-3 Keratin 5 & 6 expression in lung adenocarcinoma is not common, and when it occurs, the reaction is usually confined to small focal areas or scattered cells.1-4 The most probable cause of this finding is the presence of squamous differentiation of lung adenocarcinoma. Anti-CK 5 & 6 positivity has been useful in recognizing squamous cell carcinoma of the skin.5,6 Less than 10% of carcinomas of the breast, colon, and prostate stain positively for this marker.4 Anti-CK 5 & 6 has also been used successfully as a myoepithelial cell marker in the prostate and breast to determine malignancy.7-10 Anti-CK 5 & 6 is a useful marker to distinguish lung squamous cell carcinoma from lung adenocarcinoma and large cell carcinoma within a panel including antibodies against TTF-1, Napsin A, p63, SOX-2, desmocollin3, and desmoglein3.3,8