Lung metastasis from TTF-1 positive sigmoid adenocarcinoma. pitfalls and management

The lung is a frequent site of metastatic involvement, and in many cases the differential diagnosis between a metastasis and a primary carcinoma is a substantial question. TTF-1 is considered as a reliable marker for differential diagnosis in distinguishing primary lung carcinoma and metastasis, especially when dealing with an adenocarcinoma or a large-cell carcinoma. It was generally thought that adenocarcinomas arising in the gastrointestinal tract do not express TTF-1. Recently, it has been reported that a small percentage (1.8%-5.8%) of intestinal adenocarcinoma TTF-1 positive show differences in sensitivity/specificity depending on the antibody clones. We report a case of lung localization of a TTF-1 positive adenocarcinoma in a patient with a history of colon adenocarcinoma. Based on the current results and previous reports, we propose the following criteria for diagnosing lung metastasis from TTF-1 positive intestinal adenocarcinoma. 1) Clinical features and anamnestic history are diagnostic milestones, and provide very important information as a prognostic parameter of primary carcinoma and the time interval between the two localizations (primary and metastasis). 2) The histologic features are compatible with an enteric differentiation. 3) TTF-1 must be tested in the primary carcinoma. 4) In lung lesions, in association with TTF-1, it could be useful to test other immunohistochemical markers such as CDX-2 and NapsinA. 5) Testing other immunohistochemical or molecular markers in either lesion is not very useful. Heterogeneity between primary and metastatic lesions has been reported in the literature. Application of the above-mentioned criteria would simplify diagnosis of lung metastases from TTF-1 positive intestinal adenocarcinoma.