A tumor can form in the gastrointestinal tract, a 25-foot pathway starting from the mouth to the anus, after a change in DNA causes abnormal cells to grow.

According to Yale Medicine, gastrointestinal cancers are more likely to develop in men, and risk for the diseases increases with age. Other risk factors include smoking, alcohol consumption and an unhealthy diet, as well as underlying conditions like gastroesophageal reflux disease in the esophagus, Helicobacter pylori infection in the stomach, diabetes in the pancreas, inflammatory bowel disease in the large intestine, and hepatitis B or C virus infection or cirrhosis in the liver. Meanwhile, a small percentage of these cancers can be associated with family history or genetics.

Symptoms of gastrointestinal cancers depend on the type of cancer, and often may not occur until the disease has become more advanced.