The value of immunohistochemical expression of TTF-1, CK7 and CK20 in the diagnosis of primary and secondary lung carcinomas.

OBJECTIVES: To study the value of immunohistochemical staining of thyroid transcription factor-1 TTF-1, cytokeratin 7 CK7, and cytokeratin 20 CK20 in the differentiation between primary and secondary pulmonary carcinomas.

METHODS: Forty-three cases of lung carcinoma, 14 squamous cell carcinoma, 12 adenocarcinoma, 8 small cell carcinoma, 3 mesothelioma, and 6 metastatic tumors, were collected from the files of the Pathology Department, King Abdul-Aziz University Hospital, Jeddah, Saudi Arabia between 2004 and 2006. All cases were stained immunohistochemically following Avidin biotin method using monoclonal antibodies to TTF-1, CK7, and CK20.

RESULTS: Immunohistochemical staining of 43 cases of lung carcinoma revealed nuclear immunoreactivity for TTF-1 in all primary adenocarcinoma, and small cell carcinoma, while cases of squamous cell carcinoma were negative. Mesotheliomas were negative to TTF-1, CK7, and CK20. Metastatic tumors except for one case metastatic from the thyroid gland were negative to TTF-1. Cytokeratin 7 was positively expressed in primary tumors of lung, as well as metastatic tumors from the thyroid and breast. Cytokeratin 20 was negative in all primary lung tumors, while positive in metastatic carcinomas from the colon.

CONCLUSIONS: Thyroid transcription factor-1 is a sensitive marker for diagnosis of primary pulmonary adenocarcinoma, and differentiation between poorly differentiated squamous cell carcinoma and small cell carcinoma and adenocarcinoma. Cytokeratin 20 could be a marker for metastatic tumors from the colon to the lung since it was negative in all primary lung tumors.