Stomach cancer, also known as gastric cancer, is the accumulation of an abnormal (malignant, cancerous) group of cells that form a tumor in any part of the stomach. In most cases it refers to cancer that starts off in the mucus-producing cells on the lining of the inside of the stomach (adenocarcinoma).

According to the World Health Organization, 800,000 cancer-related deaths are caused by stomach cancer each year globally. It is the fourth most common cancer worldwide, but the second leading cause of cancer-related deaths in the world. Gastric cancer is more common among males, and people in developing nations compared to industrialized countries, the exception being Japan and South Korea, where the disease is much more common than in the USA, Canada or Europe. Signs of early stomach cancer include:

-- a painful or burning sensation in the abdomen
-- heartburn or indigestion (dyspepsia).

Other symptoms that can occur later include:
-- a sense of fullness, even after a small meal
-- nausea and/or vomiting
-- loss of appetite and/or weight loss
-- swelling of the abdomen
-- unexplained tiredness or weakness
-- blood in vomit
-- black-coloured faeces.