Stomach cancer is a disease in which cancerous cells grow in the lining of the stomach. It occurs when healthy cells in the upper digestive system become cancerous and form a tumor. This process happens slowly with stomach cancer usually developing over many years. Most people don’t show symptoms in the early stages of this disease, so it oftentimes goes undiagnosed while spreading to other parts of the body. Risk factors for stomach cancer include, people over the age of 50, men, smokers, family history of the disease, and people of Asian, South American or Belarusian descent.