Lung cancer and asbestos - 7 facts you need to know

Lung cancer develops when lung tissue cells begin to abnormally grow out of control. As the cells grow they clump together and form a tumour.

Signs and symptoms of lung cancer

The most common symptoms of lung cancer are:

• A persistent cough or a change in a cough that you have had for a long time
• Haemoptysis – coughing up phlegm with blood in it
• Pains/aches particularly when breathing or coughing
• Loss of appetite and loss of weight

Other less common symptoms of lung cancer are:

• A hoarse voice
• Difficulty swallowing
• Finger clubbing (changes in the shape of your fingers and nails)

Diagnosis and treatment of lung cancer

If you have any of the symptoms above then the best thing to do is to see your GP. You may be referred for a chest x-ray, and possibly a CT scan, which is needed to confirm the diagnosis and assist with staging the extent of the lung cancer. In some cases a biopsy may be necessary to confirm histologically that there is lung cancer and to confirm the type.

Treatment of lung cancer depends on a number of factors but most importantly the type and stage of the cancer and the age and health of the patient diagnosed. Types of treatment include surgery, radiotherapy and chemotherapy. Prognosis depends on how advanced the cancer is when it is diagnosed and the type of cancer you have.

What causes lung cancer?

Lung cancer is the second most common cancer in the United Kingdom, with around 43,500 people diagnosed in the UK each year.

The biggest cause of lung cancer continues to be smoking, with a small proportion due to second hand smoke (passive smoking). However lung cancer can also be caused by:

• Exposure to asbestos
• Exposure to other chemicals such as silica and diesel fumes
• Exposure to radon gas
• Air pollution
• A family history of lung cancer
• Previous lung disease such as tuberculosis

Lung cancer and asbestos – 7 facts you need to know

1. All types of lung cancer can be caused by asbestos exposure

   All four major histological types of lung cancer (those being squamous cell carcinoma, adenocarcinoma, small cell carcinoma and large cell carcinoma) can be related to asbestos exposure. The type of lung cancer and its location in the lung are of no significance when considering whether a person’s lung cancer is attributable to asbestos. Clinical signs and symptoms of lung cancer caused by asbestos exposure and lung cancer caused by other things do not differ.

2. A diagnosis of asbestosis is not required to prove that lung cancer has developed due to asbestos exposure

   Asbestosis is diffuse interstitial fibrosis of the lung due to exposure to asbestos dust. Asbestosis is a benign condition but can cause progressive symptoms, including breathlessness and a cough. A diagnosis of asbestosis was in the past necessary in order to prove that a lung cancer had also developed due to asbestos exposure. This is because asbestosis is generally associated with relatively high levels of exposure to asbestos. However it is now accepted that lung cancer caused by asbestos exposure can develop, even if a patient does not have asbestosis.

3. Latency is important – there is a minimum period of time between exposure to asbestos and the onset of lung cancer

   Exposure to asbestos dust does not cause lung cancer straight away. There is a minimum lag time of ten years from a person’s first exposure to asbestos to the development of lung cancer required to attribute the lung cancer to asbestos exposure.

4. Both smoking and asbestos can contribute to the development of lung cancer

   If you smoke or have smoked in the past, you are at a greater risk of developing lung cancer than a non-smoker. However, if you have also been exposed to asbestos dust you are at an even greater risk of developing lung cancer. A person who has smoked and also been exposed to asbestos has a significant risk. This is because when the two carcinogens work together the risks combine and have a multiplicative effect. This means that if, for example, a person has a 10% risk of developing lung cancer due to their smoking history and a 5% risk of developing lung cancer due to asbestos exposure, instead of having a 15% risk of developing lung cancer, they have a 50% risk of developing lung cancer because the two risks are multiplicative rather than additive. This process is known as synergy, meaning that the combination of tobacco smoke and asbestos work together to accelerate the risk of development of lung cancer.

   It is not possible to say definitively at the time of diagnosis what has caused the lung cancer and whether asbestos has contributed to its development. Sometimes patients are told that their lung cancer will be due to smoking however without detailed information regarding a person’s asbestos exposure it is simply not possible to say with any certainty whether asbestos has also played a part.

5. The greater the level of exposure to asbestos, the higher the risk of developing lung cancer

   Lung cancer is what we call a dose related disease. This means that the higher a person’s asbestos exposure, the greater risk they are at of developing lung cancer. There are some criteria in place, the Helsinki Criteria, which were formulated by an international panel of medical experts in 1977 and have since been updated. The criteria lists several factors, one or more of which can assist in proving that asbestos exposure has contributed to the development of lung cancer.

   The criteria places importance on a person’s occupational history and states that for the attribution of lung cancer to asbestos inhalation a person must have:

   (a) An estimated cumulative exposure to asbestos of 25 fibre/ml years or more. This is an engineering term. To calculate whether a person’s exposure has met this level, consideration has to be given to the type of asbestos a person was exposed to, the likely concentration of asbestos dust in the air from each task done and the length of time the task was done for.

   OR

   (b) An occupational history of one year of heavy exposure or 5-10 years of moderate exposure and at least a ten year lag time between the exposure and the onset of cancer.

   More recently, the criteria has been updated and it is now generally accepted that the 25 fibre/ml years threshold is required if a person has been exposed to predominantly amphibole asbestos fibres (blue asbestos/crocidolite and/or brown asbestos/amosite). The threshold is increased to 40 fibre/ml years if a person has had equal exposure to amphibole fibres (blue asbestos/crocidolite or brown asbestos/amosite) and serpentine fibres (white asbestos/chrysotile). Some experts consider that if a person has been exposed to purely serpentine fibres or white asbestos then a level of 100 fibre/ml years of exposure is required.

   It is important that anyone diagnosed with lung cancer who has had asbestos exposure thoroughly considers their past employment history and exposure and thinks about all of the different tasks that they did where they were exposed to asbestos. Such detailed information is necessary for an expert engineer to consider a persons likely asbestos dose

6. A post mortem examination can reveal asbestos fibres in the lungs
   
   The other method of proving that asbestos exposure caused or contributed to the development of lung cancer is based on the level of asbestos fibres in a person’s lungs. Obviously, during a persons lifetime such investigations cannot be undertaken, however upon death, if a person had lung cancer and was exposed to asbestos during their lifetime, a post mortem examination should be done. Sections of lung tissue can then be examined and asbestos fibre counts done to show the level of fibres in the lungs. If there is a certain level, as detailed in the Helsinki Criteria, this can also prove that a person’s lung cancer has been caused by asbestos exposure.
    
7. Asbestos exposure can still have caused or contributed to lung cancer, even without the presence of fibres in the lungs

   There are a number of reasons why asbestos fibre counts may show a limited level of fibres in the lungs. Chrysotile (white asbestos) breaks down and is not retained in the lungs over long periods of time. In addition there is a process called clearance in which the lungs are regularly clearing fibres. Crocidolite (blue asbestos) has a half-life clearance time of 6-7 years, meaning that the number of fibres in a person’s lungs falls by 50% each 6-7 years. The half-life for amosite (brown asbestos) is 20 years. In addition asbestos fibres and the way they are distributed in the lung tissue may be non-uniform,, meaning that it depends where the samples of lung tissue are taken from as to the fibres counted in those sections. Such issues mean that asbestos fibre counts from lung tissue may give false results even when someone has been heavily exposed to asbestos.

Asbestos and lung cancer

It is very important to consider the occupational history, any results from asbestos fibre counts undertaken following post mortem, as well as a person’s smoking history when considering the cause of lung cancer. It is no longer the case that there has also to be a diagnosis of asbestosis to prove a lung cancer has also been caused by asbestos. In addition, just because a person has smoked, it does not automatically mean that their lung cancer is due to smoking. Detailed information regarding occupational asbestos exposure is very important.