Thursday May 9 2013
The risk of lung cancer is 15 times higher in smokers
Older people with a history of smoking heavily should be offered annual low-dose CT scans to screen for lung cancer according to new US guidelines reported by the Reuters news agency.
These guidelines recommend that annual CT (computerised tomography) scans should be offered to current or former smokers aged 55-74 who have smoked 20 cigarettes a day for 30 years or more. However, screening should only be offered in facilities that can provide high standards of clinical care, the guidelines say.
Screening means testing everyone in a particular population for early stages of a disease before they have any symptoms. In the UK, screening is already in place for some cancers, such as bowel and breast cancer, but lung cancer is not currently screened for.
Mass-population screening, such as that carried out for bowel and breast cancer, is unfeasible for lung cancer because of the cost. One study has estimated that to save one lung cancer death would cost around $250,000. However, focusing resources on high-risk groups, as recommended in the US guidelines, is a more cost-efficient approach.
Heavy smokers are particularly at risk of developing lung cancer because cigarettes contain a number of cancer-causing substances (carcinogens).
Screening could be of particular use in heavy smokers because the symptoms of lung cancer often do not develop until the cancer is at an advanced stage. This makes treatment of the condition challenging.
The US guidelines point to research that suggests that these recommendations could cut rates of lung cancer deaths in smokers or ex-smokers by around 20%.
Who produced the guidelines?
The guidelines on screening have been produced by the American College of Chest Physicians.
They form part of comprehensive guidance for US doctors on the diagnosis and management of lung cancer.
What are the pros and cons of CT screening for lung cancer?
An obvious pro of CT screening for lung cancer is that it could cut lung cancer deaths. Lung cancer is one of the leading preventable causes of death in the UK and around the world.
However, no screening technique is without risk.
One risk, often overlooked, is the danger of false positives. This is where the screening test detects a sign that turns out to be harmless. In cases of lung cancer this would usually be when a lesion (abnormality in tissue) is detected, but the lesion turns out to be non-cancerous (benign).
In the general population, the rates of false positives for screening could be unacceptably high. For example, the authors say that more than 90% of nodules found by CT in the studies they looked at turned out to be benign.
This figure drops dramatically for high-risk groups, such as smokers, but one study quoted in the guidelines estimated that the false positive rate in high-risk groups could still be around one in four.
While CT scans themselves have a very low risk of causing complications, other more invasive procedures used to confirm or discount a diagnosis of lung cancer do not.
Screening could subject people to unnecessary tests that turn out to cause them harm, and there is still the possibility of false negatives. No matter how good a test is, it is likely that some cancers will be missed, leading to false reassurance.
There is also risk from radiation exposure. Although one low-dose CT scan involves only a small amount of radiation, if further imaging is required it can rapidly drive up the radiation dose patients receive.
What evidence did the guidelines look at?
The guidelines looked at evidence on the effectiveness of different methods of screening for lung cancer. These were:
- chest X-ray
- examining mucus from the airways for abnormal cells (sputum cytology)
- low-dose CT screening
The guidelines’ authors conducted a systematic review of randomised controlled trials (RCTs) and observational studies looking at the effectiveness of the different methods of screening. Most of the studies focused on middle-aged or older people with a history of smoking and, therefore, at high risk of lung cancer. In particular, they examined the death rates from lung cancer among people at high risk who were screened by low-dose CT, X-ray or sputum analysis.
The review also looked at the potential downsides of screening, including:
- the death rates, or complications resulting from further investigations of any suspected cancers, in people who had been screened
- the death rates from radiation exposure of people who had low-dose CT screening
- the rate of surgery for benign disease
What were the results?
The main finding came from one large RCT (the National Lung Screening Trial), involving more than 53,000 participants who had three annual rounds of screening. This trial showed a 20% reduction in the rate of death from lung cancer in people who were screened with low-dose CT, compared with those screened using a chest X-ray (relative risk 0.80, 95% confidence interval 0.73 to 0.93).
This trial also found that low-dose CT posed “few harms” when carried out in the context of a structured programme of care. The risk of death or major complications from further investigations into harmless conditions was between 4.1 and 4.5 per 10,000.
Other research found that using chest X-rays or sputum analysis did not reduce lung cancer deaths.
What recommendations on screening did the guidelines make?
The guidelines recommend that:
- Smokers and former smokers aged 55-74 who have smoked for 30 pack-years or more and who either continue to smoke or have quit within the past 15 years should be offered annual screening with low-dose CT.
- This should only be done in settings that can deliver the same standard of care provided to participants in the big lung cancer screening trial.
- CT screening should not be offered to people who do not meet the above criteria, say the guidelines. For example, if they are younger or older or have smoked less, since benefits outside the high-risk group are uncertain.
- Screening for lung cancer using X-rays or sputum analysis is not recommended.
What else did the lung cancer guidelines say?
The guidelines also make several other suggestions:
- Patients at risk of lung cancer should be counselled in detail about the potential benefits and risks or harms of CT screening, to help them make an informed decision.
- Screening should be conducted in centres with multidisciplinary, co-ordinated care and a comprehensive process for screening, management of findings and evaluation and treatment of potential cancers.
- Screening for lung cancer is not a substitute for stopping smoking. The guidance says “the most important thing patients can do to prevent lung cancer is not smoke”.
What is the current NHS policy regarding screening for lung cancer?
At the moment there is no national screening programme for lung cancer in the UK for the reasons outlined above.
Currently, testing for lung cancer is normally only offered to people with symptoms associated with lung cancer, such as coughing up blood or persistent unexplained weight loss. It is likely that these American guidelines will be read with interest by relevant authorities in the UK and across Europe.
The guidelines also mention additional RCTs involving 25,000 people that are underway and due to report results in 2015. These results may (or may not) provide further evidence to support the advice set out in these guidelines.
It is likely that the debate on the pros and cons of CT screening for lung cancer in high-risk groups will be discussed widely in the months to come.
Analysis by Bazian. Edited by NHS Choices. Follow Behind the Headlines on Twitter.