Stomach cancer, also called gastric cancer, is a cancer that starts in the stomach.



After food is chewed and swallowed, it enters the esophagus, a tube that carries food through the neck and chest to the stomach. The esophagus joins the stomach at the gastroesophageal junction, which is located just beneath the diaphragm (the breathing muscle under the lungs). The stomach is a sac-like organ that holds food and starts to digest it by secreting gastric juice. The food and gastric juice are mixed and then emptied into the first part of the small intestine called the duodenum.

Some people use the word stomach to refer to the area of the body between the chest and the pelvic area. The medical term for this area is the abdomen. For instance, some people with pain in this area would say they have a "stomach ache," when in fact the pain could be coming from the appendix, small intestine, colon (large intestine), or other organs in the area. Doctors would refer to this symptom as abdominal pain, because the stomach is only one of many organs in the abdomen in which cancers may start.

Stomach cancer should not be confused with other cancers that can occur in the abdomen, like cancer of the colon (large intestine), liver, pancreas, or small intestine because these cancers may have different symptoms, a different outlook, and different treatments.


Parts of the stomach

The stomach has 5 parts:



.Cardia: The upper portion (closest to the esophagus)

.Fundus: Located next to the cardia. Some cells in these areas of the stomach make acid and pepsin (a digestive enzyme), the parts of the gastric juice that help digest food.

.Body (corpus): The area between the upper and lower parts of stomach

.Antrum: The lower portion (closest to the intestine), where the food is mixed with gastric juice

.Pylorus: Acts as a valve to control emptying of the stomach contents into the small intestine.
The first 3 parts of the stomach (cardia, fundus, and body) are sometimes called the proximal stomach, and the lower 2 parts (antrum and pylorus) are called the distal stomach.

Cancers starting in different sections of the stomach may cause different symptoms and tend to have different outcomes. The cancer’s location can also affect the treatment options. Cancers that start at the gastroesophageal junction are staged and treated the same as cancers of the esophagus. A cancer that started in the cardia of the stomach but then grew into the gastroesophageal junction is also staged and treated like a cancer of the esophagus.

The stomach has 2 curves, which form its upper and lower borders. They are called the lesser curve and greater curve, respectively. Other organs next to the stomach include the colon, liver, spleen, small intestine, and pancreas.

The stomach wall has 5 layers. As a cancer grows deeper into them, the prognosis (outlook) is not as good. The innermost layer is the mucosa. This is where stomach acid and digestive enzymes are made, and where most stomach cancers start. Under this is a supporting layer called the submucosa. This is surrounded by the muscularis propria, a layer of muscle that moves and mixes the stomach contents. The outer 2 layers, the subserosa and the outermost serosa, act as wrapping layers for the stomach.


Development of stomach cancer

Stomach cancers tend to develop slowly over many years. Before a true cancer develops, pre-cancerous changes often occur in the lining of the stomach. These early changes rarely cause symptoms and therefore often go undetected.

Stomach cancers can spread (metastasize) in different ways. They can grow through the wall of the stomach and invade nearby organs. They can also spread to the lymph vessels and nearby lymph nodes. Lymph nodes are bean-sized structures that help fight infections. The stomach has a very rich network of lymph vessels and nodes. If cancer spreads to the lymph nodes, the patient's outlook is not as good. As the stomach cancer becomes more advanced, it can travel through the bloodstream and spread to organs such as the liver, lungs, and bones.


Types of stomach cancers


Adenocarcinoma

About 90% to 95% of cancerous (malignant) tumors of the stomach are adenocarcinomas. The term stomach cancer, or gastric cancer, almost always refers to adenocarcinoma. This cancer develops from the cells that form the innermost lining of the stomach (known as the mucosa).

Lymphoma

These are cancers of the immune system tissue that are sometimes found in the wall of the stomach. They account for about 4% of stomach cancers. Prognosis and treatment depend on the type of lymphoma present. For more detailed information, see our document, Non-Hodgkin Lymphoma.

Gastrointestinal stromal tumor

These are rare tumors that seem to start in cells in the wall of the stomach called interstitial cells of Cajal. Some are non-cancerous (benign); others are cancerous. Although these tumors can be found anywhere in the digestive tract, most (about 60% to 70%) occur in the stomach. For more information, see our document, Gastrointestinal Stromal Tumor (GIST).

Carcinoid tumor

These are tumors that start in hormone-making cells of the stomach. Most of these tumors do not spread to other organs. About 3% of stomach cancers are carcinoid tumors. These tumors are discussed in more detail in our separate document, Gastrointestinal Carcinoid Tumors.