The normal value of neuron-specific enolase (NSE) should be <15 μg/L. Exceeding the normal value may be caused by cancer, but the elevated value does not necessarily indicate the occurrence of cancer, and hemolysis can also lead to elevated NSE. NSE is a protease secreted by neurons and neuroendocrine cells. Some malignant tumors of neuroendocrine origin may have elevated levels of NSE, such as small cell lung cancer, neuroblastoma and pheochromocytoma. Elevated NSE levels combined with imaging evidence can be used as a basis for diagnosis and differentiation of neuroendocrine malignant tumors. For example, small cell lung cancer should be highly suspected when pulmonary localization is detected by chest CT combined with markedly elevated NSE levels. Changes in NSE levels can also be used to evaluate the effect of tumor treatment and monitor tumor recurrence or metastasis. For example, NSE levels will gradually decrease after effective treatment of neuroblastoma, but will increase again after recurrence. There is no necessary correlation between elevated NSE levels and cancer, and elevated levels do not necessarily indicate the presence of certain cancers. For example, hemolysis can release NSE, which can lead to elevated test results and affect the accuracy of the test. Patients with elevated NSE levels are advised to go to the hospital as soon as possible to have their condition evaluated by a medical professional before deciding on the next step in their treatment plan.