Markers usually refer to tumor markers, and tumor markers for small cell lung cancer are mainly gastrin-releasing peptide precursor (proGRP) and neuron-specific enolase (NSE). 1. Gastrin-releasing peptide precursor (proGRP): Gastrin-releasing peptide precursor is mainly found in the gastrointestinal tract, central nervous system and respiratory tract, and it is more stable in the blood, which is the precursor structure of gastrin-releasing peptide. The normal range in serum should be <50pg/mL. If proGRP in serum is >150pg/mL, the diagnosis of small cell lung cancer is more likely. 2. Neuron-specific enolase (NSE): neuron-specific enolase exists in neuroendocrine cells and neurons, and some data show that the positive rate of NSE in patients with small-cell lung cancer can reach 65%~100%. The normal reference range should be <16.3ng/mL. It should be noted that the reference ranges of these two tumor markers may differ according to different measurement methods, instruments or reagents, and individual hospitals or laboratories may have different reference ranges. Patients can consult their attending physician.