In our two cases, immunohistochemical staining demonstrated that the tumor cells expressed HMB45, S-100, pan melanoma and Vimentin, and did not express CK, EMA, CgA, Syn, HCG, HMW-CK, Desmin, SM-actin, TTF-1, and SCLC. The gene discussed is TTF1; the disease is small cell lung carcinoma.