Lung cancer risks and causes

• A quick guide to what's on this page
• How common lung cancer is
• Smoking and lung cancer

• Other risk factors
• Diet
• Exercise and lung cancer risk

Lung cancer is the second most common cancer in the United Kingdom (excluding non melanoma skin cancer). Around 39,000 people are diagnosed in the UK each year.

In most people, lung cancer is related to cigarette smoking. Although some people who have never smoked get lung cancer, smoking causes 9 out of 10 cases.

Here are some facts about smoking and lung cancer

• The more you smoke, the more likely you are to get lung cancer but it is the length of time you have been a smoker that is most important
• Filtered and low tar cigarettes might not increase your risk quite so much, but most smokers cancel this out by taking more, deeper puffs or smoking more cigarettes
• As soon as you stop smoking, your risk of lung cancer starts to go down
• Passive smoking (breathing in other people's cigarette smoke) increases the risk of lung cancer, but it is still much less than if you smoke yourself

It is almost impossible to work out the risk of occasional smoke exposure to second hand smoke for non smokers (passive smoking). We know that the risk of lung cancer for passive smokers goes up the more cigarette smoke they are exposed to. Overall, people exposed to environmental tobacco smoke at work or at home have their risk of lung cancer increased by about a quarter compared to people who are not exposed to environmental tobacco smoke. Heavy exposure to environmental tobacco smoke at work has been shown to double the risk of lung cancer.

Cigarette smoking is the main cause of lung cancer. But pipe and cigar smokers are still much more likely to get lung cancer than non smokers. (They are also much more likely to get cancer of the mouth or lip.)

In the past, lung cancer has always been more common in men than women. Now, as more women smoke, it is almost as common in women.

However long you have been smoking, it is always worth giving it up. Talk to your GP or practice nurse. They will be able to help and support you while you are giving up.

On CancerHelp UK we have information about organisations that help you give up smoking.

Some other things increase lung cancer risk, but they increase the risk far less than smoking.  They are

• Exposure to radon gas
• Exposure to certain chemicals
• Air pollution
• Previous lung disease
• A family history of lung cancer
• Past cancer treatment
• Lowered immunity

Exposure to radon gas

Radon gas is a naturally occurring radioactive gas that can seep out of the soil into buildings. This is more likely in certain parts of the UK where there is a lot of granite, for example in the West Country and the Peak District.  Radon is the second biggest cause of lung cancer after smoking.  The risk from radon increases the risk from smoking. Smokers with high indoor levels of radon have a particularly high risk of getting lung cancer.  If you are worried about this, the Health Protection Agency - Radiation Protection Division have information on how to check radon levels in your house.

Exposure to certain chemicals

A number of substances may cause lung cancer, including asbestos, metal dust and fumes, polycyclic aromatic hydrocarbons, diesel exhaust and silica. These are rare causes of lung cancer because you would normally only come across these chemicals in large amounts if you worked with them. And not many people do.

Air pollution

Air pollution may cause lung cancer. We know this from studies on people exposed to large amounts of diesel exhaust fumes at work for many years. This type of long term occupational exposure may increase lung cancer risk by up to 47% (that is the average risk of lung cancer, plus half again). One study has shown that people living in areas with high levels of nitrogen oxides (mainly from cars and other vehicles) have their lung cancer risk increased by about a third.

Based on a large European study, researchers think that 5 to 7% of lung cancers in non smokers are due to outdoor air pollution. In China and India, the use of coal for cooking and for heating the home, and a high level of smokiness in the home, has been shown to increase lung cancer risk. But levels of smoke in UK homes are generally much lower than in China and India.

Previous lung disease

Having had a disease that caused scarring in the lungs may be a risk factor for a type of lung cancer called adenocarcinoma of the lung. Tuberculosis (TB) can make scar tissue form in the lungs. A recent study in China showed that people who have had TB have a higher risk of lung cancer.

Chlamydia pneumoniae is a type of bacteria that can cause chest infections. Some studies have shown that people with antibodies to chlamydia pneumoniae have an increased risk of lung cancer. The antibodies show that these people have had this infection. But other studies have not shown an increased risk so we don't know for sure whether chlamydia pneumoniae can cause lung cancer.

A family history of lung cancer

Researchers are looking into the impact of family history on lung cancer. It is likely that there is at least one faulty lung cancer gene that can be passed down in families (inherited). If you have a first degree relative with lung cancer, your risk of lung cancer is doubled. It is very hard to sort out the facts here, because of the major role of smoking. Families of smokers will all be exposed to cigarette smoke and so have an increased risk of lung cancer whether they have inherited a faulty gene or not.

A study called GELCAPS investigated the possibility of a lung cancer gene. Researchers took a blood sample from diagnosed patients and one from their partner (as long as they hadn't also been diagnosed with lung cancer). This trial has recruited all the people it needs and we are waiting for the results.

Past cancer treatment

There is some evidence that particular cancer treatments might increase your risk of lung cancer. Researchers in Sweden looked at the medical records of 140,000 breast cancer patients. They found that there seemed to be an increased risk of lung cancer between 5 and 20 years after breast cancer treatment. They think this may be due to smoking after having had radiotherapy to the chest. This is backed up by the results of two studies showing particularly high risks of lung cancer in women who smoked and had radiotherapy for a previous breast cancer. The studies found no increase in risk in non smokers treated with radiotherapy for breast cancer.

Treatment for other types of cancer has also been linked to a slightly increased risk of lung cancer years later. People who have had treatment for Hodgkin's lymphoma, some types of non Hodgkin's lymphoma, or testicular cancer may have an increased risk of lung cancer. But it is important to remember that having any of these cancers is a much greater risk to your health than the slight increase in cancer risk from treatment. It is most important to get the treatment you need at the time. In some of this research, lung cancer risk seems to be increased even more in smokers, so if you have had radiotherapy to your chest it is very important not to smoke.

Previous smoking related cancers

People with a previous head and neck cancer, oesophageal or cervical cancer have an increased risk of lung cancer. But this may be explained by the fact that the risk of these cancers is higher in smokers.

Lowered immunity

HIV and AIDs lower immunity and so do drugs that people take after organ transplants. An overview of research studies shows that people with HIV or AIDS have a risk of lung cancer that is 3 times higher than people who do not have HIV or AIDS. People who take dugs to suppress their immunity after an organ transplant have double the usual risk of lung cancer.

Researchers have recently been looking into links between vitamins and lung cancer.  Fresh fruit and vegetables may help prevent cancer because they contain chemicals that can prevent cell damage, such as flavenoids and the anti oxidant vitamins A, C and E. But if you smoke, it's no good carrying on smoking and just eating a lot of fruit and veg.  The most important thing by far is to stop smoking.  Changing your diet won't reduce your risk of lung cancer much if you carry on smoking.

Researchers have looked into whether taking extra vitamin E and beta carotene may help stop smokers getting lung cancer. The body uses beta carotene to make vitamin A. Early results suggest that vitamin supplements do not help prevent lung cancer.  They may even be harmful in smokers or people who have been exposed to asbestos in the past. Another similar substance to beta carotene, called beta cryptoxanthin, is found in fruits such as oranges and mangoes. It may lower lung cancer risk, but we don't know how it affects smokers yet. Having enough selenium in your diet may also help lower lung cancer risk, but the evidence for this isn't completely clear as researchers have measured selenium levels in different ways in different trials.

So, for now the advice on diet is the same as for preventing cancer other chronic diseases generally. We should all try to

• Eat more fresh fruit and vegetables
• Cut down on fat (particularly animal fats)
• Eat less salt and sugar
• Cut down on alcohol

One overview of published research showed that people taking more exercise had a lowered risk of lung cancer compared to inactive people. But since then, the large European Prospective Study into Cancer and Nutrition (EPIC) has found no evidence that overall activity levels affect lung cancer risk.  Another large study found that exercise only lowered risk in smokers and ex-smokers. Research into this area is continuing.