CY211 is an indicator that does not confirm a diagnosis of cancer, regardless of how high it is, and can only be used as a reference indicator. It is generally used to detect lung cancer, but it may also be elevated in other malignant tumors, such as gastric cancer, so it is not possible to determine whether it is lung cancer or gastric cancer based on the indicator alone. Therefore, it is necessary to find out the occupying lung lesion by chest CT and further do percutaneous lung aspiration biopsy or bronchoscopy for pathology to confirm whether it is lung cancer. If it is gastric cancer, gastroscopy must be done and pathology can be obtained through gastroscopy to confirm. CY211 has a high diagnostic value and relatively high specificity for non-small cell lung cancer. If this index is higher, it may be lung cancer or non-small cell lung cancer, which requires further improvement of lung CT and other examinations. Therefore, it is more significant for lung cancer screening or surgery, and follow-up examination after chemotherapy.