The classic early epidemiological study by Doll and Hill in 1950 was followed by the ‘doctors’ study in which the smoking patterns and health outcome of 20,000 British doctors were followed for 50 years – a unique achievement. This study and others have demonstrated unequivocally that: smoking causes lung cancer; the risks are proportional to the dose; quitting reduces that risk; but that even after quitting additional risks remain for more than 40 years.
The lifetime risk of a continuing smoker developing lung cancer is approximately 1 in 15, whereas for a lifelong non-smoker it is 1 in 200–300. If people quit at 50 years of age they reduce their lifetime risk to approximately 1 in 30. One consequence of this is that the proportion of lung cancer occurring in ex rather than current smokers in the UK is increasing, and is now at about 50%.
There is no such thing as a ‘safe cigarette’. Smokers become very proficient at controlling their preferred nicotine dose. For example, they can achieve a quick increase in levels by taking several deep inhalations when anxious or can opt for lower sustained levels when bored. The increasing use of low-tar cigarettes and filters may be responsible for the rise in frequency of adenocarcinoma, as the smoke is inhaled further out into the lung as the smoker tends to inhale more deeply. As a proportion of all cancers, this particular form has increased from about 15 to 30% in the last 20 years. The risk of lung cancer for long-term pipe smokers and the habitual cigar smoker is lower, but these forms of smoking do also cause cancer.
Risk Factors Additional To Active Tobacco Smoking
The rates of spontaneous lung cancer increase with age and account for about 10% of all forms. Some lung cancers never seem to be associated with tobacco. An example is bronchoalveolar-cell carcinoma (BAC), which mimics a chronic unresolvable pneumonia. These tumors spread within the lung segment or lobe and the majority do not metastasis.
The most important additional risk factors are passive smoking and asbestos. There is strong epidemiological evidence that the relative risk to long-term passive smokers is 20–30% above baseline for a spouse or partner, and higher for workplace exposure, and that this causes about 600 lung cancer deaths yearly in the UK. This underpins the banning and restriction of smoking in the workplace and enclosed public places, which is already in force in several American states, some European countries, Scotland and, more recently, England.
People with symptomatic pulmonary asbestosis secondary to occupational exposure, have a 500% increase in their risk of lung cancer. There is a debate as to whether this risk is confi ned to persons with asbestosis, or whether asbestos itself is a carcinogen. Although unresolved it is likely that asbestos does increase the risk on its own and in proportion to the intensity and duration of exposure.
Radon is a naturally occurring radioactive gas that leaches out of granite. Therefore, people living in houses built upon granite are at an increased risk. This is of considerable importance in countries such as Sweden, and to a lesser extent in the south-west of the UK and in Wales.
Women are more susceptible to lung disease, including both chronic obstructive pulmonary disease (COPD) and lung cancer, as a result of smoking than men; the reason for this is unknown. This fact makes it even more important for us to develop primary prevention strategies that are effective in young women. Lung cancer is currently the fastest increasing cause of cancer death in women, yet in the UK 38% of females aged between 20 and 24 years are regular smokers.
People with COPD are at an increased risk of developing lung cancer compared to others with an equivalent smoking history but normal spectrometry, and the risk is roughly proportional to COPD severity. The reason for this is unknown. It has been hypothesized that it may be due to the additional effects of a separate tobacco-induced airway inflammation or, less plausibly, to the effects of altered airflow rates on carcinogen deposition in peripheral lung tissue.
Lung Cancer Prevention
Prevention is by far the most effective way by which we could reduce lung cancer mortality. However, primary prevention is weak in the UK: by the age of 15, one in every four children is a regular smoker and it is estimated that 450 children start smoking every day. It is at this time that nicotine addiction develops.
Altering this pattern of behaviour will be difficult. It will probably need a combination of social and pricing policies and social pressures. Government action taken in Europe and the USA includes cigarette and tobacco packet health warnings, banning tobacco advertisements in all media, health education and, most recently, a ban on smoking in all public places. Parental habits and peer pressure appear to be the two driving factors in most cases and are far less susceptible to alteration.
Nicotine is highly addictive. Mark Twain famously said ‘quitting smoking is the easiest thing in the world to do; I have done it several times.’ Thus, although more than 70% of smokers would like to quit, long-term quit rates remain low. Simple unequivocal advice by a doctor produces a quit rate of 1–3%. If nicotine replacement therapy and support are added, the quit rate rises to about 6–8%. However, this action tends to be concentrated on adults over the age of 50. Because young people consult their physicians less often, the impact on younger smokers is less. Quit programmes cost £800 per life-year saved (1998 data); lung cancer chemotherapy is about 25 times as expensive.
International agencies both in the EU and worldwide, such as the World Health Organization (WHO), are attempting to combat the menace of the active promotion of cigarette smoking by the large multinational tobacco companies. The WHO Framework Convention on Tobacco Control (FCTC) is an example of this action (Box 1.4). It remains to be seen whether concerted regulatory action by the world’s governments will be powerful enough to halt the trend of increased smoking in developing countries, which threatens to engulf fledgling health services and result in a huge burden of tobacco-related diseases in the second half of the 21st century and beyond.
