The gastrointestinal (GI) tract, or digestive tract, includes the mouth, pharynx (throat), esophagus, stomach, liver, pancreas, gallbladder, small intestine, and large intestine. The tissues that line these different organs can give rise to a variety of malignant tumours.
From the mouth to the esophagus, the lining is made up of epithelial cells called squamous cells. The esophagus is then lined with glandular cells that produce some of the enzymes necessary for digestion, and these cells go on to line the stomach and intestines.
Squamous cells give rise to squamous cell carcinoma, and glandular cells to adenocarcinoma – these being the most common types of cancers in the GI tract. The other organs, such as the pancreas, gallbladder, and liver have specialized tissues that serve unique functions in the digestive process.
Information taken from GI Cancer Institute.