TTF1 and non-small cell lung carcinoma: The presence of TTF-1 is usually assessed to confirm the diagnosis of primary non-small cell lung carcinoma (especially adenocarcinoma) [10]; the purpose of TTF-1 staining in our particular case was to decide whether the low cuboidal metaplastic bronchiolar epithelium observed in the pathological specimens derived from the pre-existing bronchiolar epithelium, because it is known that TTF-1 is only expressed on the normal epithelium of the lung and thyroid [10].