No one knows why some people develop stomach cancer and others don't. The number of people affected varies widely between different countries. For example, stomach cancer is far more common in Japan than in the UK. There is also evidence that people from poorer backgrounds are at increased risk.

There are a many other factors that increase the risk of developing stomach cancer.

• Age. Stomach cancer is most common around the age of 60. It's rare under the age of 40.
• Gender. Men are around twice as likely to develop stomach cancer as women.

• Diet. A diet high in salt and foods that are smoked or cured may increase the risk of stomach cancer. In particular, certain food preservative chemicals known as nitrosamines, which are found cured meats such as bacon and ham, may increase your chance of developing stomach cancer.
• Family history. Some people inherit an increased risk of developing stomach cancer.
• Type A blood group. Some research indicates that people who have type A blood are at higher risk of developing stomach cancer.
• Smoking. When you smoke, you swallow small amounts of tobacco smoke, which increases your risk of getting stomach cancer.
• Atrophic gastritis. This condition causes the lining of the stomach to waste away. It has also been linked with an increased risk of stomach cancer.