About Stomach Cancer
Stomach cancer usually begins in cells in the inner layer of the stomach. Over time, the cancer may invade more deeply into the stomach wall. A stomach tumor can grow through the stomach’s outer layer into nearby organs, such as the liver, pancreas, esophagus, or intestine.
Stomach cancer cells can spread by breaking away from the original tumor. They enter blood vessels or lymph vessels, which branch into all the tissues of the body. The cancer cells may be found in lymph nodes near the stomach. The cancer cells may attach to other tissues and grow to form new tumors that may damage those tissues.
Prevalence of Stomach Cancer
Cancer is a leading cause of death worldwide, accounting for 7.6 million deaths (around 13% of all deaths) in 2008. Of the 7.6 million deaths, gastric cancer accounts for 740,000; exceeded only by lung cancer (1.4 million deaths).
In the United States, an estimated 21,000 new gastric cancer cases were diagnosed in 2010.
Early stomach cancer often does not cause symptoms. As the cancer grows, the most common symptoms are: 
- Discomfort or pain in the stomach area
- Difficulty swallowing
- Nausea and vomiting
- Weight loss
- Feeling full or bloated after a small meal
- Vomiting blood or having blood in the stool
Studies have found the following risk factors for stomach cancer: 
- Helicobacter pylori infection: H. pylori is a bacterium that commonly infects the inner lining (the mucosa) of the stomach. Infection with H. pylori can cause stomach inflammation and peptic ulcers. It also increases the risk of stomach cancer, but only a small number of infected people develop stomach cancer.
- Long-term inflammation of the stomach: People who have conditions associated with long-term stomach inflammation (such as the blood disease pernicious anemia) are at increased risk of stomach cancer. Also, people who have had part of their stomach removed may have long-term stomach inflammation and increased risk of stomach cancer many years after their surgery.
- Smoking: Smokers are more likely than nonsmokers to develop stomach cancer. Heavy smokers are most at risk.
- Family history: Close relatives (parents, brothers, sisters, or children) of a person with a history of stomach cancer are somewhat more likely to develop the disease themselves. If many close relatives have a history of stomach cancer, the risk is even greater.
- Poor diet, lack of physical activity, or obesity:
- Studies suggest that people who eat a diet high in foods that are smoked, salted, or pickled have an increased risk for stomach cancer. On the other hand, people who eat a diet high in fresh fruits and vegetables may have a lower risk of this disease.
- A lack of physical activity may increase the risk of stomach cancer.
- Also, people who are obese may have an increased risk of cancer developing in the upper part of the stomach.
Most people who have known risk factors do not develop stomach cancer. For example, many people have an H. pylori infection but never develop cancer. On the other hand, people who do develop the disease sometimes have no known risk factors.