CA19-9 is clinically one of the commonly used tumor markers on, it has no specificity, and lesions of multiple systems can cause abnormal CA19-9. The abnormal increase of CA19-9 is mainly caused by two reasons: malignant tumors and benign lesions, malignant tumors such as pancreatic cancer, gastric cancer, etc. A decrease in CA19-9 indicates that the lesion causing the increase in CA19-9 is under control, whether it is a malignant tumor or a benign lesion, indicating that the patient’s condition is improving. Patients should also review CA19-9 values and related imaging examinations regularly after CA19-9 decreases until the condition is stable in the long term.