Stomach cancers are usually found when a person goes to the doctor because of signs or symptoms they are having. If stomach cancer is suspected, tests will be needed to confirm the diagnosis.
Signs and symptoms of stomach cancer

Unfortunately, early-stage stomach cancer rarely causes symptoms. This is one of the reasons stomach cancer is so hard to detect early. The signs and symptoms of stomach cancer can include:

  • Poor appetite
  • Weight loss (without trying)
  • Abdominal (belly) pain
  • Vague discomfort in the abdomen, usually above the navel
  • A sense of fullness in the upper abdomen after eating a small meal
  • Heartburn or indigestion
  • Nausea
  • Vomiting, with or without blood
  • Swelling or fluid build-up in the abdomen

Most of these symptoms are more likely to be caused by things other than cancer, such as a stomach virus. They may also occur with other types of cancer. But people who have any of these problems, especially if they don’t go away or get worse, should check with their doctor so the cause can be found and treated.
Since symptoms of stomach cancer often do not appear until the disease is advanced, only about 1 in 5 stomach cancers in the United States is found at an early stage, before it has spread to other areas of the body.

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http://www.cancer.org/cancer/stomach...ncer-diagnosis