Stomach cancer (also called gastric cancer) starts in the stomach. The illustration below shows the stomach and other parts of the digestive system.

In everyday speech, the word "stomach" is often used to refer to the area of the body between the chest and the hips. For instance, people with pain in the appendix, small intestine, colon, or gallbladder might say they have a "stomach ache." The medical term for this area is the abdomen and doctors would describe the symptom as "abdominal pain."

The difference is important because the stomach is only one of many organs in the abdomen that can develop cancer. So stomach cancer should not be confused with other cancers that can occur in the abdomen. These other cancers can cause different symptoms. They are treated differently and have a different outlook for survival (prognosis).

The Stomach

After food has been chewed and swallowed, it passes down a tube called the esophagus (ee-sof-uh-gus) and empties into the stomach. The stomach is a sack-like organ that holds food and mixes it with gastric juice to begin the process of digestion.

Cancer can start in any part of the stomach. Symptoms, treatment options, and the outlook for survival can all vary depending on where in the stomach the cancer begins.

The stomach itself is made up of 5 layers. It helps to know about these layers because as cancer grows deeper into them, the outlook for the patient gets worse. Starting from the inside and working out, the innermost layer is called the mucosa. This is where the stomach acid and digestive juices are made. Next is a supporting layer called the submucosa. This is surrounded by the muscularis, a layer of muscle that moves and mixes the stomach contents. The next 2 layers, the subserosa and the serosa (the outermost layer) act as wrapping for the stomach.

Stomach Cancer

Most of the time stomach cancer starts in the mucosa and slowly grows out into the other layers. Stomach cancer tends to grow slowly over many years. Before a true cancer develops, there are usually changes that take place in the lining of the stomach (the mucosa). These early changes rarely cause symptoms and often are not noticed.

How it Spreads (Metastasizes)

Stomach cancer can spread in several different ways. It can grow through the wall of the stomach and invade nearby organs. It can also spread to the lymph nodes (bean-sized collections of immune system cells) and then through the lymph system. If cancer spreads this way, the outlook for a cure gets worse. When stomach cancer is more advanced, it can travel through the bloodstream and form deposits of cancer cells in organs such as the liver, lungs, and bones. But even though it has spread to other organs, it is still called stomach cancer.

Adenocarcinoma

Most cancers of the stomach are of a type called adenocarcinomas. This cancer develops from cells that form the lining of the innermost layer, the mucosa. The term "stomach cancer" almost always refers to this type of cancer.

Other Stomach Tumors

Lymphomas, gastrointestinal stromal tumors (often called GIST), and carcinoid tumors are other, much less common, tumors that are found in the stomach. The treatment and outlook for these cancers are different from that of adenocarcinoma and are not covered here.