| GUIDELINES |
|Year : 2008 | Volume : 3 | Issue : 6 | Page : 65-67 |
|Epidemiology of lung cancer |
Yasser Bahader1, Abdul-Rahman Jazieh2
1 King Faisal Specialist and Research Center, Riyadh, Saudi Arabia
2 King Abdulaziz Medical City for National Guard, Riyadh, Saudi Arabia
Department of Oncology (Mail code 1777), King Abdulaziz Medical City for National Guard, P.O. Box 22490, Riyadh 11426
| Abstract || || |
Lung cancer ranks first in the world in incidence and mortality. Multiple risk factors have been identified and the majority of lung cancer cases are preventable.
This manuscript presents a summary of the epidemiology of lung cancer and the risk factors.
Keywords: Lung cancer, epidemiology, risk factors
|How to cite this article: |
Bahader Y, Jazieh AR. Epidemiology of lung cancer. Ann Thorac Med 2008;3:65-7
Lung cancer is the most common cancer worldwide (1.35 million of 10.9 million of new cases) and the deadliest cancer (1.18 million of 6.7 million cancer-related deaths). 
As per the Saudi National Cancer Registry 2003 statistics, there were 242 cases of lung cancer accounting for 3.7 % of all diagnosed cases.  Lung cancer ranked fifth among the male population and 15th among the female population. It affected 183 (75.6%) males and 59 (24.4%) females, with a male to female ratio of 3:1. The overall Adjusted Standard Rate (ASR) was 3.1/100,000. The ASR was 4.7/100,000 for males and 1.4/100,000 for females, which is much less than the international figures. For example, ASR in the United States is 87/100,000 for males and 54.4/100,000 for females. The mean age at diagnosis was 64 years among males (range 24-98 years) and 61 years among females (range 24 - 89 years). The most common morphological subtypes are squamous cell carcinoma, adenocarcinoma and small cell carcinoma, which accounted for 25, 23 and 13%, respectively. Stage distribution showed that 54.5% had distant metastasis at presentation, and localized disease, regional and unknown represent 17.4, 14.5 and 13.6%, respectively.
| Risk Factors for Lung Cancer || || |
The rapid increase of lung cancer over the last century from a rare disease to an epidemic is attributed to the exposure to newly introduced major risk factors, which includes smoking at the top of the list.
Around 85 - 90% of lung cancer could be attributed to the use of tobacco directly or indirectly. 
The relative risk of dying from lung cancer is 11 - 20 times more in smokers compared with nonsmokers. The risk of lung cancer is dependent on the number of cigarettes smoked per day (calculated by pack/year number) and the duration of smoking, with an increase in the risk of smoking started at a younger age. ,,
The environmental tobacco exposure (ETS), which may be referred to as 'second-hand smoking,' increases the risk by 27-80%. ,,, ETS may occur at home or at work. For example, the risk of nonsmoker spouse increases by 20 - 30% if the spouse is a smoker over a nonsmoker's spouse.  About 25% of the lung cancer in nonsmoker is attributed to second-hand smoking, which constitutes about 5% of all lung cancer cases.
Smoking cessation at any age is of proven benefits of reduction of lung cancer risk over an extended period of time (15-20 years), but it remains higher than never-smoker risk. ,,,
The exposure to radon is an established risk factor of lung cancer, which was initially observed in uranium miners. , However, this naturally occurring radioactive gas accumulates also in buildings and homes, especially in basements and lower-level floors.
The exposure to the indoor radon may be responsible for up to 9% if lung cancer in Western countries as it has a synergistic effect with smoking. Smoking in minors increases the risk of lung cancer by 10 times over the nonsmoker minors. 
Industrial and occupational exposure
Exposure to various carcinogens has been linked to lung cancer. The list of these carcinogens includes arsenic, polycyclic hydrocarbons, diesel exhaust, herbicides and insecticides, silica, asbestos, beryllium and chromium. Asbestos is a well known cause of not only mesothelioma but also of primary lung cancer. The risk of exposure to asbestos is about five times more than the general population, but when it is combined with smoking, a synergetic effect takes place and increases the risk up to 50 - 100 times. The incidence peak of cancer occurs 25 - 30 years after exposure. ,,,
Exposure to outdoor pollution, especially nitrogen oxides from the traffic fumes, has been linked to an increase risk of lung cancer. ,
| Other Risk Factors || || |
There are other risk factors that were associated with an increase in the incidence of lung cancer, including family history, sedentary life, alcohol and dietary factors, with a variable strength of association. ,,,
Lung cancer is divided into non small cell lung cancer (>80% of cases) and small cell lung cancer. The non small cell lung cancer is divided into adenocarcinoma, squamous cell and large cell carcinoma.
There was a shift in the incidence of squamous cell carcinoma and adenocarcinoma. Up to the late 1980s, squamous cell lung cancer was the most common subtype, which was then surpassed by adenocarcinoma.
It is note worthy that the risk of all of these subtypes of cancer is increased by smoking.
As mentioned earlier, smoking cessation and eliminating the risk of tobacco will eradicate the majority of lung cancer cases, making it one of the most preventable cancers. ,, Minimizing the occupational exposure to the above-mentioned carcinogens will decrease the risk further.
Various studies using chest X-ray, sputum cytology and spinal computed tomography (CT) scans were not supportive of routine mass screening. ,, A large multisite NCI-USA sponsored study of spinal CT scan including more than 50,000 participants may help answer this question.
| Conclusion || || |
While lung cancer is the leading cancer in incidence and mortality, it is also a preventable disease in the majority of cases.
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