Smoking and Lung Cancer

Everyone knows that smoking causes lung cancer. But how big are your risks of getting lung cancer if you smoke and what is it about tobacco smoking that causes lung cancer?

For some illnesses caused by smoking, smokers have a 50% or a 100% greater chance if getting that illness than never smokers. Stomach cancer and pneumonia are like that. A 100% greater risk doesn’t mean 100% chance of getting the illness, it means double the chances of getting the illness as compared with the chances if you never smoked.

For lung cancer, the increased risks are much greater. So a man who continues to smoke until he dies is has 2300% increased risk of dieing of lung cancer: I.e. he is 23 times more likely to die of lung cancer, as compared with if he had never smoked. Of course, the overall size of that risk is influenced by how common the disease is. A lifelong non-smoker has less than half of one percent chance of dieing of lung cancer by the age of 75. A smoker who quits smoking by age 40 has a 6% chance of dieing of lung cancer by age 75. If the smoker keeps smoking until they die or reach age 75, then they have a 16% cumulative risk of dieing of lung cancer. These risks are amazingly big, when one remembers that for the smoker to get lung cancer they also have to survive and not be killed by one of the other common illnesses caused by smoking (e.g. COPD, heart-attack etc).

Smoking causes lung cancer because the smoke itself contain known carcinogenic chemicals such as benzo(a)pyrene and NNK. As these chemicals are deposited into the lungs year on year they cause DNA damage, oxidative stress and inflammation, which promote the initiation and growth of tumors. It is essentially the DNA damage, and the inability of the body to repair that damage, that results in cells starting to divide and multiply in a deviant way that ends up growing into a malignant tumor. Because the lungs are such essential organs for life (ie. healthy lungs are necessary for breathing) and because lung cancer is not easy to detect and cure at an early stage, lung cancer is very often fatal, with a 5-year survival rate around 15%. In many cases the cancer metastasizes and affects other organs of the body.

Great efforts continue to try to develop new methods of detection and cure for lung cancer. But right now the best interventions we have are those that prevent it occurring in the first place, by reducing initiation of smoking or enabling addicted smokers to quit before they develop lung cancer. By far the best thing you can do to dramatically reduce your risks of developing lung cancer, is to avoid all inhalation of tobacco smoke.

If you are interested in reading about the health effects of smoking in greater detail I recommend a recent chapter on that topic by Foulds and colleagues (2008) that can be downloaded from: http://www.tobaccoprogram.org/staffarticles.htm