Papillary thyroid carcinoma usually shows the expression of typical immunohistochemical markers such as TG, TTF-1 and Pax8, etc. However, in metastatic thyroid cancer with pleural effusion, the absence of thyroid markers can occur (4, 5), and the expression of NapsinA can also occur in pericardial effusion (9), which confounds the diagnosis. The gene discussed is TTF1; the disease is differentiated thyroid carcinoma.