ENO2 and small cell lung carcinoma: Tumor-associated proteins, such as cytokeratin 19 fragment (CYFRA 21-1) and carcinoembryonic antigen (CEA) for NSCLC [108] or neuron specific enolase (NSE) for SCLC [109], have proved their benefit only in addition to clinical, radiological, or histological suspicion of lung cancer and only on a qualitative level.