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About 95% of stomach cancers are adenocarcinomas. Adenocarcinomas of the stomach originate from the glandular cells of the stomach lining.
In the United States, adenocarcinoma of the stomach occurs in about 21,000 people each year and causes almost 11,000 deaths per year. It is more common among certain populations: people aged 50 and older, blacks, Hispanics, and American Indians. For unknown reasons, adenocarcinoma of the stomach is becoming less common in the United States. Worldwide, stomach cancer is the second most common cancer. It is far more common in Japan, China, Chile, and Iceland. In these nations, screening programs are an important means of early detection.
Causes and Risk Factors
Adenocarcinoma of the stomach often begins at a site where the stomach lining is inflamed. Infection with the bacterium Helicobacter pylori is the cause of most stomach cancer. People who have certain gene mutations are also at risk.
Stomach polyps may become cancerous (malignant) and are thus removed. Adenocarcinoma of the stomach is particularly likely to develop if the polyps consist of glandular cells, if the polyps are larger than ¾ inch (2 centimeters), or if several polyps exist.
Certain dietary factors were once thought to play a role in the development of adenocarcinoma of the stomach. These factors included a high intake of salt, a high intake of carbohydrates, a high intake of preservatives called nitrates (often present in smoked foods), and a low intake of fruit and green leafy vegetables. However, none of these factors has proved to be a cause.
Symptoms
In the early stages, symptoms are vague and easily ignored. Early symptoms may mimic peptic ulcer disease, with burning abdominal pain. Therefore, peptic ulcer symptoms that do not resolve with treatment may indicate stomach cancer. The person may notice a feeling of fullness after a small meal (early satiety).
People may begin to feel full after eating sooner than they normally do. They may have weight loss or weakness caused by difficulty eating or by an inability to absorb some vitamins and minerals. Anemia, characterized by fatigue, weakness, and light-headedness, may result from very gradual bleeding that causes no other symptoms, from malabsorption of vitamin B12 (a vitamin needed for red blood cell formation), or from malabsorption of iron (a mineral needed for red blood cell formation) due to a lack of stomach acid. Uncommonly, a person may vomit large amounts of blood (hematemesis) or pass black tarry stools (melena). When adenocarcinoma is advanced, a doctor may be able to feel a mass when pressing on the abdomen.
Even in the early stages, a small adenocarcinoma may spread (metastasize) to distant sites. The spread of the tumor may cause liver enlargement, a yellowish discoloration of the skin and the whites of the eyes (jaundice), fluid accumulation and swelling in the abdominal cavity (ascites), and swollen lymph nodes. The spreading cancer also may weaken bones, leading to bone fractures.
Diagnosis
Endoscopy (an examination in which a flexible tube is used to visualize the inside of the digestive tract) is the best diagnostic procedure. It allows a doctor to view the stomach directly, to check for Helicobacter pylori, and to remove tissue samples for examination under a microscope (biopsy). Barium x-rays are used less often because they rarely reveal small early-stage cancers and do not allow for biopsy.
If cancer is found, people usually have a computed tomography (CT) scan of the chest and abdomen to determine the extent to which the tumor has spread to other organs. If the CT scan does not show the tumor has spread, doctors usually perform an endoscopic ultrasound (which shows the lining of the digestive tract more clearly because the probe is placed on the tip of the endoscope) to determine the depth of the tumor and the involvement of nearby lymph nodes.
Prognosis and Treatment
Fewer than 5 to 15% of people with adenocarcinoma of the stomach survive longer than 5 years. The cancer tends to spread early to other sites. If the cancer is confined to the stomach, surgery is usually performed to try to cure it. Removal of the entire tumor before it has spread offers the only hope of cure. Most or all of the stomach and nearby lymph nodes are removed. The prognosis is good if the cancer has not penetrated the stomach wall too deeply. In such cases, up to 80% of people may survive for 5 years. However, in the United States, the results of surgery are often poor, because most people have extensive cancer by the time a diagnosis is made. In Japan, where stomach cancer is very common, mass public health screening programs help to detect it early so that a cure is more likely. Chemotherapy and radiation therapy may help in certain circumstances.
If the cancer has spread beyond the stomach, surgery cannot cure the condition, but it is sometimes used to relieve symptoms. For example, if the passage of food is obstructed at the far end of the stomach, a bypass operation, in which an alternate connection is made between the stomach and the small intestine, allows food to pass. This connection relieves the symptoms of obstruction—pain and vomiting—at least for a while. Chemotherapy plus radiation therapy may help relieve symptoms as well but does little to help people survive longer than 5 years.
Last full review/revision February 2013 by Elliot M. Livstone, MD
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