TTF1 and small cell carcinoma: Thyroid transcription factor-1 (TTF-1), a positive regulator of surfactant protein promoter activity, has emerged as a major and sensitive marker for a lung cancer, but is not up to differentiate the different entities of pulmonary cancer, such as adenocarcinoma, large-cell neuroendocrine carcinoma, small-cell carcinoma or carcinoid (Folpe et al, 1999; Barlési et al, 2005).