The exact causes of cancer of the stomach are still unknown, although research is being done to try to find the cause. Over the past 30 years the number of people who develop stomach cancer has fallen, especially in Western countries. Although the reason for this is unknown, it is thought to be related to changes in our diet, particularly the use of refrigeration, which has meant that people eat more fresh food and less smoked and pickled food.

Cancer of the stomach is more common in men, particularly in their 60s and 70s. Factors that can increase the risk of stomach cancer include:

• pernicious anaemia, which affects the lining of the stomach and results in a lack of vitamin B12.
• atrophic gastritis – a stomach disorder
• helicobacter pylori (H pylori) – an infection that affects the stomach
• a hereditary condition in which people have small growths (polyps) in their stomach
• Barrett's oesophagus – a condition where abnormal cells develop in the lining of the lower end of the gullet or the place where the gullett joins the stomach (the gasto-oesophageal junction). It is not a cancer, but over a long period of time a small number of people with this condition may develop cancer of the gullet or stomach.