For example, the sensitivity of detecting circulating tumor antigens, such as CA125, CA199, neuron specific enolase (NSE), carcinoembryonic antigen (CEA), and cytokeratin 19 fragment (CYFRA 21–1) is only 5.0%, 4.9%, 19.7%, 17.2%, and 26.5%, respectively, in patients with stage I NSCLC (31). The gene discussed is ENO2; the disease is neoplasm.