Cancer starts when cells in the body begin to grow out of control. Cells in nearly any part of the body can become cancer, and can spread to other areas of the body. To learn more about how cancers start and spread, see What Is Cancer? Stomach cancer, also called gastric cancer, starts in the stomach. To understand stomach cancer, it helps to know about the normal structure and function of the stomach.
After food is chewed and swallowed, it enters the esophagus, a tube that carries food through the throat and chest to the stomach. The esophagus joins the stomach at the gastroesophageal (GE) junction, which is just beneath the diaphragm (the thin sheet of 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 “stomachache”, when in fact the pain could be coming from the appendix, small intestine, colon (large intestine), or other organs in the area. Doctors would call this symptom abdominal pain, because the stomach is only one of many organs in the abdomen.
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 can have different symptoms, different outlooks, and different treatments.
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 inner lining (mucosa) of the stomach. These early changes rarely cause symptoms and therefore often go undetected.
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. For example, cancers that start at the GE junction are staged and treated the same as cancers of the esophagus. A cancer that starts in the cardia of the stomach but then grows into the GE junction is also staged and treated like a cancer of the esophagus. (For more information, see Esophagus Cancer.)
Types of stomach cancers
Adenocarcinoma
Most (about 90% to 95%) cancers of the stomach are adenocarcinomas. A stomach cancer or gastric cancer almost always is an adenocarcinoma. These cancers develop from the cells that form the innermost lining of the stomach (the mucosa).
Lymphoma
These are cancers of the immune system tissue that are sometimes found in the wall of the stomach. The treatment and outlook depend on the type of lymphoma. For more detailed information, see Non-Hodgkin Lymphoma.
Gastrointestinal stromal tumor (GIST)
These rare tumors start in very early forms of cells in the wall of the stomach called interstitial cells of Cajal. Some of these tumors are non-cancerous (benign); others are cancerous. Although GISTs can be found anywhere in the digestive tract, most are found in the stomach. For more information, see Gastrointestinal Stromal Tumor (GIST).
Carcinoid tumor
These tumors start in hormone-making cells of the stomach. Most of these tumors do not spread to other organs. These tumors are discussed in more detail in Gastrointestinal Carcinoid Tumors.
Other cancers
Other types of cancer, such as squamous cell carcinoma, small cell carcinoma, and leiomyosarcoma, can also start in the stomach, but these cancers are very rare.
When you have cancer you might hear about other ways to treat the cancer or treat your symptoms. These may not always be standard medical treatments. These treatments may be vitamins, herbs, special diets, and other things. You may wonder about these treatments. Some of these are known to help, but many have not been tested. Some have been shown not to help. A few have even been found to be harmful. Talk to your doctor about anything you’re thinking about using, whether it’s a vitamin, a diet, or anything else. You can’t change the fact that you have cancer. What you can change is how you live the rest of your life – making healthy choices and feeling as good as you can.