Introduction
The stomach is a muscular bag with a capacity of about 1 liter or quart. It lies along the digestive tract between the esophagus and the small intestine. The stomach serves as a reservoir for food eaten during meals and begins the process of digestion. Its inner walls are composed of glands that secrete acid and digestive enzymes.

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 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.  This is important because the stomach is only one of many organs in the abdomen. The stomach has 5 sections. The upper portion (closest to the esophagus) is called the cardia. Next to this is the fundus. 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. The lower portion (closest to the intestine) includes the antrum, where the food is mixed with gastric juice, and the pylorus, which acts as a valve to control emptying of the stomach contents into the small intestine. The area between the proximal and distal stomach is the body (corpus) of the stomach. The upper parts of the stomach (cardia, fundus, and body) are sometimes called the proximal stomach, and the lower two (antrum and pyloris) are called distal stomach.

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 has 5 layers. It is important to know about these layers because as a cancer grows deeper into them, the prognosis (outlook for survival) 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, a layer of muscle that moves and mixes the stomach contents. The next 2 layers, the subserosa and the outermost serosa, act as wrapping layers for the stomach.

Stomach cancers can spread, or 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 lymph nodes. Lymph nodes are bean-sized structures near many body 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 outlook for survival is not as good. When the stomach cancer becomes more advanced, it can travel through the bloodstream and spread to organs such as the liver, lungs, and bones.

Synonyms and Keywords
Adenocarcinoma of the stomach, adenocarcinoma, gastric carcinoma, carcinoma of the stomach, stomach carcinoma, neoplastic disease of the stomach, pernicious anemia.

Stomach Cancer Starts in the Stomach
The stomach is only one of many organs in the abdomen in which cancers may start. Stomach cancer should not be confused with cancers of the colon (large intestine), liver, pancreas, or small intestine because these cancers may have different symptoms, a different outlook, and different treatments.

Types of Cancers in the Stomach

Adenocarcinoma: The most common form stomach (gastric) cancer that affects the stomach is 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.  Adenocarcinoma arises in the glands of the innermost layer of the stomach. This tumor tends to spread through the wall of the stomach and from there into the adjoining organs (pancreas and spleen) and lymph nodes. It can spread through the bloodstream and lymph system to distant organs (metastasize).

Carcinoid tumor: These are tumors that start in hormone-making cells of the stomach. Most of these do not spread to other organs. About 3% of stomach cancers are carcinoid tumors.

Gastrointestinal stromal tumor (GIST): 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 (70%) occur in the stomach.

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 whether the lymphoma is aggressive or is a slow-growing MALT lymphoma.

Prevalence
The incidence and death rates for stomach cancer have decreased markedly during the past 60 years. In 1930, stomach cancer was the leading cause of cancer-related deaths among American men. Since then, the death rate in men from stomach cancer in the United States has dropped from 28 to 5 per 100,000 people. However, stomach cancer is the second leading cause of cancer death worldwide (source: http://web.mit.edu/newsoffice/2008/stomach-0501.html)

Causes/ Risk Factors
Stomach cancer remains the second most frequent cause of cancer-related death worldwide, with particularly high frequencies in Japan, China, Korea, parts of Eastern Europe, and Latin America.

No one knows the exact causes of stomach cancer. Doctors often cannot explain why one person develops this disease and another does not. However research has shown that people with certain risk factors are more likely than others to develop stomach cancer. A risk factor is something that may increase the chance of developing a disease. Studies have found the following risk factors for stomach cancer:

• Race. Stomach cancer is 1.5-2.5 times more common in African American, Hispanic, and Native American people than in white.
• Socioeconomic status.  People of low socioeconomic status are more likely to develop stomach cancer. This may be related to diet and/ health screening.
• Sex. Men are more likely than women to develop stomach cancer.
• Blood Type. People with blood type A re more likely to develop stomach cancer.
• Age. Advanced age – two-thirds of people who have it are over age 65
• Family history. A family history of stomach cancer increases risk.
• Prior diagnosis of pernicious anemia. People with a prior diagnosis of  pernicious anemia (a chronic progressive disease caused by the failure of the body to absorb vitamin B-12) are more likely to develop stomach cancer than those who have not been diagnosed with pernicious anemia.
  
• Smoking: Research shows that people who smoke are more likely to develop stomach cancer than people who do not smoke.
• Diet: Studies suggest that people who eat a diet high in foods that are smoked, salted, or pickled may be at increased risk for stomach cancer. On the other hand, eating fresh fruits and vegetables may protect against this disease.
• Prior treatment of benign stomach or duodenal ulcer disease. Research shows that removal of part of the stomach is associated with an increased risk of cancer developing in the remaining stomach, especially at least 15 years after the surgery. It is currently suggested that people who had portions of their stomachs removed 20 years ago or longer should receive yearly endoscopies. This is because of the increased risk of stomach cancer following such surgery.
• Helicobacter pylori infection:  H. pylori is a type of bacteria that commonly lives in the stomach. Helicobacter pylori, is a common cause of chronic gastritis and peptic ulcer disease. H. pylori infection increases the risk of stomach inflammation and stomach ulcers. It also increases the risk of stomach cancer, but only a small number of infected people develop stomach cancer. Although H. pylori infection is now recognized as the major cause of both peptic ulcers and gastric cancer, and has been classified as a group I carcinogen by the World Health Organization, physicians are not sure whom to screen and treat with costly antibiotics, aside from first degree relatives of gastric cancer patients and those with peptic ulcer disease.

Note: most people who have known risk factors do not develop stomach cancer. For example, many people have H. pylori in their stomach but never develop cancer. On the other hand, people who do develop the disease sometimes have no known risk factors.

If you think you may be at risk, you should talk with your doctor. Your doctor may be able to suggest ways to reduce your risk and can plan a schedule for checkups.

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.

Cancers starting in different sections of the stomach may cause different symptoms and tend to have different outcomes.

• Feeling of fullness after taking only a small amount of food
• Discomfort in the stomach area
• Difficulty swallowing because of a tumor involving the upper part of your stomach, near the esophagus
• Nausea and vomiting
  

• Fatigue
• Weight loss
• Iron deficiency anemia
• Overt blood loss - Vomiting blood or a material that looks like coffee grounds or passing black stools
• Severe nausea and vomiting - A late symptom caused by blockage of the stomach drainage by the enlarging cancer

Anyone with these symptoms should tell the doctor so that problems can be found and treated as early as possible.

• Physical exam: The doctor checks your abdomen for fluid, swelling, or other changes. The doctor also feels for swollen lymph nodes. Your skin and eyes are checked to see if they seem yellow.
• Upper GI series: Often used first to diagnose issues because it causes less discomfort than other screening tools. The doctor orders x-rays of your esophagus and stomach. The x-rays are taken after you drink a barium solution. The solution makes your stomach show up more clearly on the x-rays.  Although this procedure can be effective in detecting stomach cancers, is not as effective as other diagnostic tools (like a biopsy and endocopy) in detecting small tumors.  Any suspicious areas seen on barium study always require further endoscopic checking.
• Endoscopy: The doctor uses a thin, lighted tube (endoscope) to look into your stomach. The doctor first numbs your throat with an anesthetic spray. You also may receive medicine to help you relax. The tube is passed through your mouth and esophagus to the stomach. Gastrointestinal (GI) endoscopy is superior because it allows a direct view of the area of concern.
• Biopsy (tissue sampling): The doctor uses an endoscope to remove tissue from the stomach. A pathologist checks the tissue under a microscope for cancer cells. A biopsy is the only sure way to know if cancer cells are present.
  

• Computed tomography (CT) scan of the abdomen. Computed tomography (CT) is a medical imaging method employing tomography.  CT is a sensitive method for diagnosis of abdominal diseases. It is used frequently to determine stage of cancer and to follow progress.  Oral and/or rectal contrast may be used depending on the indications for the scan. A dilute (2% w/v) suspension of barium sulfate is most commonly used. The concentrated barium sulfate preparations used for fluoroscopy e.g. barium enema are too dense and cause severe artifacts on CT. Other agents may be required to optimize the imaging of specific organs, such as rectally administered gas (air or carbon dioxide) or fluid (water) for a colon study, or oral water for a stomach study.subjects patients to much higher levels of ionizing radiation, so it is used infrequently.Chest x-ray film.
• Nuclear bone scans: These may be helpful in ruling out advanced disease that has spread outside your stomach walls.
  

• People with advanced heart and lung disease may not tolerate aggressive therapy.
• In many cases, the stomach cancer may have advanced too far for any available treatment to work.

Prognosis
If your cancer is found at an early stage of development, your chance of long-term survival approaches 70%.

If you have advanced stomach cancer, your chance for recovery is poor.  Factors that point to poor recovery include the following:

• Presence of cancer in your lymph nodes
• Involvement of distant organs
• Tumors involving the upper one third of your stomach

The number of stomach cancers has decreased because of the following:

• Improved socioeconomic standards
• Widespread use of refrigeration for food preservation
• Adoption of diets rich in fruits and vegetables
• Eliminating Helicobacter pylori infections in people

In areas where frequency of stomach cancer remains high, such as Japan, screening programs that include upper GI barium studies and, more recently, gastrointestinal endoscopy have improved survival rates. These screenings enable doctors to find more cases at an early stage of development. This increases survival rates.