Smoking and Lung Cancer Risk Magnitude
A 60 year old man has smoked one pack daily since age 20. During counselling he asks how his risk of lung cancer compares with that of a lifelong nonsmoker of the same age. His chest radiograph is clear and he has no respiratory symptoms. Approximately how many times higher is his lung cancer risk?
- A.About two times
- B.About five times
- C.About fifteen timesCorrect
- D.About fifty times
Explanation
Sustained cigarette smoking increases lung cancer risk roughly fifteenfold compared with never smoking, with estimates in heavy long term smokers reaching twenty to thirty fold. Duration of smoking is a more powerful determinant than daily intensity, which is why starting in adolescence is so damaging. This very large relative risk contrasts sharply with the approximately twofold increase in myocardial infarction risk, and examiners frequently test the difference. Risk falls progressively after cessation but never returns to that of a never smoker, which is why former smokers remain eligible for screening. Low dose computed tomography screening is recommended annually for adults aged 50 to 80 years with at least a 20 pack year history who currently smoke or quit within the past 15 years. This man has a 40 pack year history and therefore meets screening criteria, and a normal chest radiograph does not exclude early disease because plain films are inadequate for screening. Smoking causes not only lung cancer but also cancers of the larynx, oesophagus, bladder, kidney, pancreas, stomach, cervix and myeloid leukaemia. Cessation counselling should accompany any screening discussion.
Why each option
- A.
- A twofold increase corresponds to coronary risk, not to the far larger lung cancer risk.
- B.
- Fivefold substantially underestimates the association between sustained smoking and lung cancer.
- C.
- Correct. Lung cancer risk in sustained smokers is on the order of fifteen times that of never smokers.
- D.
- Fiftyfold exceeds published estimates even for the heaviest long term smokers.
Reference: US Preventive Services Task Force. Screening for Lung Cancer. JAMA. 2021;325(10):962-970; Surgeon General Report, The Health Consequences of Smoking, 2014
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