Causes and risk factors of stomach cancer

The exact cause of stomach cancer is unknown, but risk factors can increase the chance of a person developing it.

What are risk factors?

The exact cause of stomach cancer is unknown. But things called risk factors can increase the chance of a person developing it. Having a risk factor does not mean you will get stomach cancer. And if you do not have any risk factors, it does not mean you will not get stomach cancer.

Stomach cancer is not infectious. You cannot pass it on to other people.

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Stomach cancer is more common in men than in women. Men are twice as likely than women to get stomach cancer.


The risk of developing stomach cancer increases as you get older. Over half of people (51%) diagnosed with stomach cancer are aged 75 or older.

Helicobacter pylori (H. pylori) infection

This is a stomach infection that causes inflammation of the stomach lining. Over a long time, it can increase the risk of cancer developing.


Smoking increases the risk of stomach cancer. The longer a person smokes for and the more they smoke, the greater the risk. The risk reduces when you stop smoking.


Diet can affect the risk of stomach cancer. The following things can increase your risk:

  • not eating enough fresh fruit and vegetables
  • having too much salt in your diet
  • eating a lot of processed meats
  • eating foods that are smoked or pickled.

The number of people in the UK who develop stomach cancer is decreasing. This is probably because our diet is improving and we are eating more fresh foods.

Being overweight

People who are very overweight have an increased risk of cancer in the area where the stomach joins the oesophagus. This area is called the gastro-oesophageal junction (GOJ).

Stomach conditions

Some stomach conditions can increase the risk of developing stomach cancer.

Changes to the stomach lining

Some medical conditions can cause changes to the stomach lining. This can increase your risk of stomach cancer. These conditions include the following:

  • Pernicious anaemia

    Cells that line the stomach make something called intrinsic factor (IF). This helps us to absorb vitamin B12 and make red blood cells. Pernicious anaemia causes the immune system to attack the cells that make IF. If you are not making enough IF, you do not absorb enough vitamin B12. This means you have too few red blood cells (anaemia).

  • Atrophic gastritis

    This is a chronic inflammation of the stomach lining.

Stomach surgery for another condition (such as an ulcer)

Removing part of the stomach reduces the amount of acid your stomach makes. This means you have less protection from bacteria, which can increase the risk of stomach cancer.

Family history and risk of cancer

Most stomach cancers are not caused by inherited cancer genes. And most people who develop stomach cancer do not have a strong family history of it. But sometimes stomach cancer runs in families. This may be because close family members share some risk factors for stomach cancer. For example, they may eat a similar diet or have H. pylori infection. Rarely, it is caused by an inherited gene.

In general, the chance of there being a family link is greater when:

  • a number of family members have been diagnosed with stomach cancer
  • the family members who have been diagnosed with stomach cancer are closely related
  • the family members were diagnosed with stomach cancer at a younger age.