UTILITY OF CYTOKERATIN IMMUNOSTAINING IN SEPARATING PULMONARY ADENOCARCINOMAS FROM COLONIC ADENOCARCINOMAS

Adenocarcinomas of uncertain origin are a frequent problem for surgica l pathologists. To determine the utility of immunostaining for cytoker atin 7 and cytokeratin 20 in the separation of pulmonary adenocarcinom as from colonic adenocarcinomas, we studied routinely processed, forma lin-fixed tissue from 151 of these tumors using commercially available monoclonal antibodies and an avidin-biotin immunohistochemical techni que. Used alone, neither cytokeratin 7 immunostaining or cytokeratin 2 0 immunostaining reliably separated these tumors. However, the immunop henotype of cytokeratin 7 positive/cytokeratin 20 negative was seen in 86% of the pulmonary adenocarcinomas, and in 0% of the colonic adenoc arcinomas. Conversely, the cytokeratin 7-negative/cytokeratin 20-posit ive immunophenotype was seen in 77% of the colonic carcinomas, and in 0% of the pulmonary tumors. In conclusion, cytokeratin 7/cytokeratin 2 0 immunostaining patterns may be helpful in separating pulmonary adeno carcinomas from colonic adenocarcinomas.