Utility of thyroid transcription factor-1 and cytokeratin 7 and 20 immunostaining in the identification of origin in malignant effusions.

To estimate the utility of thyroid transcription factor-1 (TTF-1) and the combined cytokeratin 7 (CK7) and 20 (CK20) immunoprofile as a marker for identifying the primary site of metastatic adenocarcinoma in effusions of the serous cavity. Formalin-fixed, paraffin-embedded cell block specimens of pleural and peritonealfluid diagnosed as metastatic adenocarcinomas with known sites of origin were used for TTF-1, CK7 and CK20 immunohistochemistry. The primary sites of these cases were lung (16 cases), ovary (15), stomach (9), colon (8) and breast (8) and were confirmed by radiologic and/or histologic evaluation. The lung adenocarcinomas showed TTF-1 positivity in 81% (13/16) of cases. All nonpulmonary adenocarcinomas lacked TTF-1 staining. The CK7-/CK20+ immunophenotype was seen in 63% of colonic adenocarcinomas and not seen in lung, ovary, stomach or breast adenocarcinomas. The CK7+/CK20- immunophenotype was seen in 100%, 88% and 87% of cases that originated in the lung, breast and ovary, respectively. TTF-7 immunostaining is useful in the differentiation between pulmonary and nonpulmonary origin of adenocarcinomas in malignant effusions. The combination of CK7-/CK20+ immunostaining is useful in identifying colon adenocarcinomas.