Risk Factors
Cigarette smoking is the major cause of lung cancer in both men and women. It is estimated that cigarette smoking accounts for about 90% of lung cancer in men and 85% in women (Blot and Fraumeni, 1996). There is evidence that the risk of lung cancer associated with a given level of cigarette smoking may be higher in women than in men. Epidemiological evidence indicates that passive inhalation of cigarette smoke results in an increase in the incidence of bronchogenic carcinoma. Indoor air pollution from tobacco smoke causes more lung cancer than outdoor air pollution.
Studies have also demonstrated that several carcinogenic substances encountered in the workplace cause lung cancer, including asbestos, arsenic, nickel and chromium compounds, polycylic hydrocarbons, and silica. Environmental exposure to radon and low intake of dietary retinoids may also increase the risk of developing lung cancer (Blot and Fraumeni, 1996). Patients with head and neck cancer (excluding nasopharyngeal carcinoma), patients with resected non-small cell lung cancer are at risk of developing second primaries.
Recently, attention has focused on hereditary predisposition as a potential cause of lung cancer. Several case-control studies have shown an elevated risk of lung cancer among blood relatives of affected persons after adequate control for smoking, however, the risk was often diagnosed on the basis of death registrations or reports of family members, which may be unreliable. Since there are many carcinogens in tobacco smoke, the pathways controlled by the cytochrome P450 gene family, responsible for detoxification of xenobiotics are being studied. However because many of these genes (e.g. CYP1A1) are strongly inducible, and because lung cancer patients frequently stop smoking after diagnosis, studies of the importance of these genes have been difficult. At the present time, no data exists to suggest that genetic screening will prevent lung cancers.
Prevention
Cessation of cigarette smoking would clearly prevent the majority of lung cancer. There is evidence that diet high in fresh vegetables and fruits may lower the risk. Secondary prevention by pharmacological treatment to reverse a recognisable premalignant lesion is under investigation at the British Columbia Cancer Agency. A standard approach does not exist at this time.
Tobacco Control
Lung cancer is largely preventable as 80-90% of all cases are related to smoking. For children and adolescents, the focus should be on not starting smoking, whereas for adults, smoking cessation is an effective method of reducing lung cancer risk, but it is difficult to implement and achieve. Even if cigarette smoking were eradicated quickly, the lung cancer problem would persist for many years. Currently, 50% of lung cancers are seen in former smokers. Even if all tobacco induced lung cancers were eliminated, lung cancer would still be the 5th or 6th most common cause of cancer mortality. Unfortunately, demographic data on the smoking behaviour of British Columbians continues to show an unacceptable prevalence of tobacco use.
Physicians can help to reduce cigarette smoking and lung cancer in the following ways.
| a) |
Set an example by not smoking. |
| b) |
Display and promote "anti-smoking" information. |
| c) |
Take a careful smoking history on all patients and counsel smoking patients to stop even if they are well. Physician counselling is one of the most effective interventions. |
| d) |
Be familiar with the methods and pharmacology of nicotine replacement therapies as an adjunct to counselling. |
| e) |
Be aware of the non-smoking advice and programs available through the Canadian Cancer Society, British Columbia Lung Association and the British Columbia Medical Association. |
| f) |
Assist those who are promoting legislation to restrict all cigarette advertising, control indoor air pollution and increase tobacco taxes. |
| g) |
Be aware of industrial and environmental hazards, which may be related to lung cancer. |
Key References:
- National Cancer Institute of Canada. Canadian Cancer Statistics 1998. Toronto: NCIC, 1998.
- National Cancer Institute of Canada. Canadian Cancer Statistics 1995. Toronto: NCIC, 1992.
- Blot W, Fraumeni JF Jr. Cancers of the lung and pleura. In: Schottenfeld D, Fraumeni JF Jr. (Eds.). Cancer Epidemiology and Prevention. 2nd Ed 1996. Oxford University Press. pp637-665.
- International Association for the Study of Lung Cancer. Tobacco policy recommendations of the international association for the study of lung cancer: a 10 point program. IASLC Charter, 1994.