What is stomach cancer?
Stomach cancer (also called gastric cancer) starts in the stomach. The picture below shows the stomach and other parts of the digestive system. To understand stomach cancer, it helps to know about the normal structure and function of the stomach.
Stomach or abdomen?
In everyday speech, the word “stomach” is often used to refer to the part 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 pain as “abdominal pain.”
The difference is important because the stomach is only one of many organs in the abdomen that cancer can start in. So stomach cancer should not be confused with cancers in other organs in the same area. These other cancers can cause different symptoms. They are treated differently and have a different outlook for survival (prognosis).
After food has been chewed and swallowed, it passes down a tube called the esophagus and goes 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 all depend on where the cancer starts in the stomach.
The stomach wall has 5 layers. It helps to know about these layers because as cancer grows deeper into them, the outlook for the patient gets worse. These are the 5 layers, working from the inside out:
- The innermost layer is called the mucosa. This is where stomach acid and digestive juices are made. It is also where most stomach cancers start.
- The next layer is the submucosa.
- A layer of thick muscle called the muscularis propria moves and mixes the stomach contents.
- The outer 2 layers, the subserosa and the serosa, act as wrapping for the stomach.
Growth of 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 starts, there are usually changes that take place in the inner lining of the stomach (the mucosa). These early changes rarely cause symptoms and often are not noticed.
Cancers starting in different sections (as opposed to layers) of the stomach may cause different symptoms, tend to have different outcomes, and may call for different treatment options. To find out more about the different sections of the stomach, please see our document Stomach Cancer.
How stomach cancer spreads
Stomach cancer can spread in different ways. It can grow through the wall of the stomach and into nearby organs. It can also spread to nearby lymph nodes (bean-sized collections of immune system cells) and then spread through the lymph system. When stomach cancer is more advanced, it can travel through the bloodstream to other organs like the liver, lungs, and bones. If the cancer has spread, the patient’s outlook is not as good.
Types of cancers in the stomach
By far, most cancers of the stomach are a type called adenocarcinomas. This cancer starts from cells that form the lining of the innermost layer, the mucosa. The terms stomach cancer or gastric cancer almost always refers to this type of cancer.
Other stomach tumors
Lymphomas, gastrointestinal stromal tumors (often called GISTs), 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. The ACS has separate information about these cancers. Please see our documents, Non-Hodgkin Lymphoma, Gastrointestinal Stromal Tumor, or Gastrointestinal Carcinoid Tumors.
The rest of the information here refers only to adenocarcinoma of the stomach.
Last Medical Review: 03/18/2013
Last Revised: 04/22/2014