TTF1 and small cell lung carcinoma: In addition, TTF-1, which can be detected in different histologic subtypes of lung carcinomas24, 25, 26, 27, is also expressed in almost 85–90% of SCLC tumor cells22; moreover, CD56 (NCAM), a cell surface sialoglycoprotein, is specifically expressed in neuroendocrine tissues and tumors, including SCLC28, 29.