Prolonged abdominal pain with no apparent cause and unexplained weight loss may be a warning of a gastrointestinal tumor Published on 02/08/2022 The symptoms of gastrointestinal tumors vary greatly and depend on the type of tumor and where it is located, so they must be studied individually. Although colorectal cancer is the most common, the incidence of other gastrointestinal tumors, like pancreatic or stomach tumors, has increased in recent years. Risk factors for gastrointestinal tumors include a poor diet, physical inactivity, alcohol consumption and smoking