Objective: Thyroid transcription factor-1 (TTF-1) immunoexpression is frequently determined in small-cell lung carcinomas, as well as primary lung adenocarcinomas. While dealing with metastatic carcinomas, TTF-1 immunoexpression is a significant indicator of primary lung carcinomas. Recent studies have revealed that TTF-1 immunoexpression is also defined in non-lung cancers, such as squamous cell carcinomas of different sites and certain neuroendocrine tumors. The verified data obtained from

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... se studies indicate that a straightforward diagnosis of primary lung carcinoma in cases with positive TTF-1 immunoexpression can cause diagnostic contradictions. The aim of our study is to investigate the immunoexpression status of TTF-1 in common non-lung tumors. Methods: A total of 85 cases that were diagnosed in our institute between the years 2011-2012 were included in our study. After a review of the pathological slides prepared from these tumors [colon adenocarcinoma (n: 15), renal cell carcinoma (n: 15), prostate adenocarcinoma (n: 15), invasive papillary urothelial carcinoma (n: 15), invasive ductal carcinoma of breast (n: 15), and neuroendocrine tumors (n: 10)] TTF-1 immunohistochemistry was applied. Semiquantative evaluation based on the distribution and intensity of the staining was performed by two pathologists, respectively. Results: Positive immunostaining was evident in only 1 case of colon adenocarcinoma out of 85 cases. Conclusion: Our study demonstrated that TTF-1 immunoexpression is a very rare finding (1%) in non-lung tumors. This result provides that anti-TTF-1 is a reliable antibody in the interpretation of primary lung carcinomas. In fact, further studies with a large number of cases are needed to confirm the sensitivity and specificity of TTF-1.