Description: Anti -TTF-1 antibody is useful in differentiating primary adenocarcinoma of the lung from metastatic carcinomas from the breast, mediastinal germ cell tumors and malignant mesothelioma. It can also be used to differentiate Small cell lung carcinoma from lymphoid infiltrates. Loss of TTF-1 expression in non -small cell lung carcinoma has been associated with aggressive behavior of such neoplasms.