CA199 is one of the tumor markers, mainly reflecting digestive tract tumors such as pancreatic cancer, gastric cancer, colorectal cancer, so with the improvement of the condition of gastric cancer, pancreatic cancer or colorectal cancer, CA199 can be decreased to normal. If CA199 is obviously elevated before surgery or radiotherapy, but with radical surgical resection or radiotherapy, the tumor will be controlled, CA199 will be obviously decreased or even normal, but once recurrence or distant metastasis occurs, CA199 will be elevated again. Therefore, CA199 can indicate the diagnosis of the disease or the progress of disease recurrence. It is worth noting that CA199 is not a diagnostic indicator, the diagnosis of GI tumors must be found in the pathology of cancer cells, and CA199 is only an indicator of the progress of the disease.