Stomach cancer risks and causes

Stomach cancer is now the 13th most common cancer amongst adults in the UK. About 7,600 cases are diagnosed each year. Out of every 200 cancers diagnosed, 5 are cancer of the stomach (2.5%). Roughly twice as many cases are diagnosed in men as in women.

Like most cancers, stomach cancer becomes more common as people get older. 95 out of every 100 cases (95%) are diagnosed in people aged 55 or older. The CancerHelp UK section about how a cancer starts explains why this is.

The incidence of stomach cancer in the UK has fallen a great deal since the 1970s. This is probably partly due to better diet.

Incidence varies from country to country around the world. This may be explained to some extent by differences in diet. A diet high in very salty foods increases the risk of stomach cancer. Stomach cancer levels are very high in Japan where very salty pickled foods are popular. But these foods are not typically eaten in the UK and stomach cancer rates here are lower than in Japan.

A diet high in certain preserved foods may also increase your risk. Several studies and a large ongoing research study called EPIC have found a small increase in the risk of stomach cancer in people who eat a lot of preserved meat. Preserved meat includes bacon, sausages and ham. These meats contain chemicals called nitrosamines, which are known to cause cancer in animals. A Canadian study found that the increased risk was greatest in people infected with Helicobacter pylori bacteria. Some studies show a higher risk of stomach cancer in people with high levels of nitrosamines in their diet. Eating a lot of pickled foods may also increase the risk.

A recent study showed that vegetarians may have a lower risk of stomach cancer than meat eaters. And the EPIC study showed an increased risk of stomach cancer for people who eat a lot of red meat. But we need more studies to confirm this. 

A diet high in fresh fruit and vegetables seems to reduce the risk of stomach cancer. This may be because these foods contain high levels of antioxidant vitamins. Vitamin C in particular, together with other substances in these fresh foods, may help to prevent damage to the stomach lining that can lead to cancer. Vitamin A has been shown to protect against stomach cancer. One study has also suggested that vitamin B6 may have a protective effect. Research studies have shown that antioxidant vitamins may have the greatest protective effect in people who are under nourished. Antioxident vitamins help in well nourished people too, but their effects are likely to be less. This may explain why some recent studies in America and Europe found no association between fruit and vegetable intake and stomach cancer risk.

In the UK only about 1 in 3 adults eat enough fruit and vegetables - the recommended minimum of 5 portions a day. So there is a lot we can do to eat our way to a healthier life. If you are worried about cancer or heart disease, you could take a look at your diet and see if you can improve it. You'll find some tips in the healthy eating section of our News and Resources website.

Helicobacter pylori is a bacterial infection that has been investigated a lot in the past few years. Infection with this type of bacteria increases the risk of stomach cancer in the lower part of the stomach. Most studies show that helicobacter pylori (HP) infection could double the risk of stomach cancer. Infection with a particular type of HP called 'cagA positive helicobacter pylori' can increase the risk even more.

Millions of people are infected with these bacteria and most of those do not get stomach cancer so other factors must also be at work. Diet and smoking may interact with HP to cause stomach cancer. The bacteria can cause an inflammatory condition called severe chronic atrophic gastritis (SCAG) and this can lead to stomach cancer. People with SCAG have an increased risk of stomach cancer in both the upper and lower parts of the stomach.

Helicobacter infection can be shown on a blood test or a breath test. It can usually be cured fairly easily with a course of antibiotic treatment. But we're not really sure yet how much benefit we get from getting rid of it. HP may protect against a particular type of cancer of the food pipe (oesophagus) called adenocarcinoma of the oesophagus. A meta analysis of studies looking at HP treatment showed that it lowered the risk of stomach cancer a little bit but it may be most effective in people with peptic ulcer or precancerous changes. Even if you do have it treated, there is a chance that you will get re infected because it is so common. So your doctor may not treat HP unless you have stomach pains (a symptom of peptic ulcer). 

Cigarette smoke contains many cancer causing chemicals. When you breathe in cigarette smoke, you will always swallow some of it without meaning to. In that way, smoking can increase the risk of stomach cancer. About 1 in 5 stomach cancers (20%) in the UK is thought to be caused by smoking.

People who smoke have around twice the risk of stomach cancer compared to non smokers. The risk falls if you stop smoking. If smokers have HP infection, they may have more than 10 times the risk of non smokers without HP infection.

A Swedish study showed that non smokers who use a type of chewing tobacco called snus increase their risk of stomach cancer by up to a half.

From recent research it seems unlikely that drinking alcohol increases the risk of stomach cancer.

A rare condition called FAP (familial adenomatous polyposis) may increase the risk of stomach cancer. This is an inherited condition (you are born with it) where many polyps grow throughout the lining of the digestive system. It is known to increase the risk of bowel cancer. Most of these polyps are not serious and don't increase stomach cancer risk. But a type of polyp called an adenomatous polyp can go on to develop into cancer. Another rare type of polyp called a leiomyoma can also develop into a type of cancer called a gastrointestinal stromal tumour (GIST).

Acid reflux is where acid from the stomach goes back up into the oesophagus. It can cause inflammation of the oesophagus (oesophagitis). Acid reflux and oesophagitis increase the risk of stomach cancer. Acid reflux is also called gastro oesophageal reflux disease (GORD). Stomach cancer risk is increased in people who have severe GORD or who have had surgery to treat the resulting changes in the cells that line the food pipe. Changes to these cells are called Barrett's oesophagus.

Some diseases and operations have been shown to increase the risk of stomach cancer because they lower the amount of acid produced in the stomach. The reduced acid level may allow more bacteria to grow and the bacteria may help to produce more nitrites and nitrosamines - chemicals that may increase stomach cancer risk. The diseases and operations include

• Pernicious anaemia
• Having part of the vagus nerve removed (vagotomy)
• Having had part of your stomach removed (partial gastrectomy)

If you've had a stomach ulcer in the past, your risk of stomach cancer is doubled. If you have a stomach ulcer and have surgery, your risk lowers again. If you've had an ulcer in the small bowel (a duodenal ulcer) your risk of stomach cancer is likely to be lower than average. This may be because duodenal ulcers are caused by too much stomach acid and the acid protects you against stomach bacteria.

An overview of published studies showed that people who regularly take non steroidal anti inflammatory drugs appear to have a slightly lower risk of stomach cancer. These drugs are called NSAIDs. Examples are aspirin, ibuprofen or Nurofen. Researchers in 2010 reviewed the trials looking at whether daily aspirin can protect against health conditions. They found that taking daily aspirin may reduce the risk of dying from stomach cancer. This needs more research though, and regular use of NSAIDs can increase the risk of developing stomach or duodenal ulcers.

Family history is being looked at as a risk factor for stomach cancer. Brothers, sisters, and children, of people with stomach cancer have an increased risk of getting it themselves. We're not sure whether this is genetic, or because they share other risk factors, such as Helicobacter pylori infection.

Researchers have found that some Maori families from New Zealand have a particular faulty gene (mutated gene) more often than the general population. This changed gene makes developing stomach cancer more likely. A person from a family with the gene mutation has a 70% chance of getting stomach cancer at some point in their life. Often, people with this mutation who get stomach cancer develop it at a young age. They may be in their 30's rather than their 70's, which is a more usual age for stomach cancer. It is early days for this research and we don't yet know if there are any other inherited genetic mutations for stomach cancer.

Statistically, men have a slightly increased risk of stomach cancer if they've already had prostate cancer, breast cancer, bladder cancer or testicular cancer. Women have an increased stomach cancer risk if they've had ovarian cancer, breast cancer or cervical cancer. Both sexes have increased risk if they've had food pipe (oesophageal) cancer, non melanoma skin cancer, bowel cancer, non Hodgkin's lymphoma or thyroid cancer.

Atomic bomb survivors in the 2nd World War were more likely to get stomach cancer because of the radiation they were exposed to. And we've known for many years that people who have had radiotherapy to the spine for a condition called ankylosing spondylitis have an increased risk.

Stomach cancer has also been linked to medical X-ray exposure in the past. These days, the amount of radiation used in a regular X-ray is much lower than it used to be. But some other medical tests, such as CT scans, use a significant amount of radiation. This is not harmful to you if you have scans only when you need them. But it explains why doctors are reluctant to use scans for routine screening.

People with suppressed immune systems due to infection with HIV, AIDS, or drugs taken following an organ transplant, have double the risk of stomach cancer compared to other people.

Studies show that people with a higher body mass index have an increased risk of adenocarcinoma in the upper area of the stomach. Being overweight increases the risk of acid reflux and gastric oesophageal reflux disease, which increase the risk of stomach cancer.

Some studies show a higher risk of stomach cancer in people who are exposed at work to dust from metal, mining, quarrying or stone cutting. One study has shown an increased risk in people exposed to diesel exhaust fumes in their work. One study of uranium miners exposed to radon showed a small increase in stomach cancer risk.

One study has shown that in women who take hormone replacement therapy (HRT) the risk of stomach cancer is half that of women who do not take HRT.

Some recent studies have shown that people doing the highest amounts of physical activity in their work and leisure time can reduce their risk of stomach cancer by up to a half.