The National Cancer Center published the “Guidelines for Lung Cancer Screening and Early Detection and Treatment in China (2021, Beijing)” in 2021. In it, the main risk factors for lung cancer in China are summarized as follows
1. Smoking and Passive Smoking
Smoking is currently recognized as the most important risk factor for lung cancer. Cigarettes form more than 60 types of carcinogens during the lighting process. Nitrosamines, polycyclic aromatic hydrocarbons, and benzo(a)pyrene in tobacco are highly carcinogenic to the respiratory system.
In 1985, the World Health Organization’s International Agency for Research on Cancer identified smoking as the cause of lung cancer. The relationship between smoking and the risk of lung cancer is related to the type of tobacco, the age of starting smoking, the number of years of smoking, and the amount of smoking. In a meta-analysis of published literature on smoking and lung cancer in China, the risk of lung cancer was 2.77 times higher in smokers than in nonsmokers (ratio: 2.77, 95% confidence interval: 2.77).
95 confidence interval: 2.26 to 3.40).
Passive smoking is also a risk factor for the development of lung cancer, mainly in women. The association between passive smoking and lung cancer was first reported in the early 1980’s. In a 2003 Meta-analysis of 22 workplace studies of tobacco exposure and lung cancer risk, Stayner et al. showed that non-smoking workers had a 24 increased risk of lung cancer due to passive smoking in the work environment (relative risk ratio = 1.24, 95 confidence interval: 1.18 to 1.29), while in workers with high exposure to environmental tobacco smoke was 2.01 (95 confidence interval: 1.33-2.60), and the duration of exposure to environmental tobacco smoke was strongly associated with lung cancer.
2. History of chronic obstructive pulmonary disease (COPD)
Chronic obstructive pulmonary disease (COPD) is an airway pathology caused by chronic inflammation that can lead to alveolar destruction, narrowing of the bronchial lumen, and irreversible pulmonary dysfunction at the end stage. In a systematic search and Meta-analysis of published studies exploring the strength of the association between COPD and lung cancer in China and abroad since 1995, the risk of lung cancer in patients with COPD was 1.43 times (relative risk rate: 1.43, 95 confidence interval: 1.14-1.81) and 1.57 times (relative risk rate: 1.57, 95 confidence interval) higher than in those without COPD in case-control studies and cohort studies, respectively. (relative risk rate: 1.57, 95 confidence interval: 1.20 to 2.05).
3. Occupational exposure
A variety of specific occupational exposures can increase the risk of lung cancer, including asbestos, radon, beryllium, chromium, cadmium, nickel, silicon, soot, and soot.
Lenters et al. conducted a Meta-analysis of 19 articles on asbestos and lung cancer published from 1950 to 2009, which showed that the risk of lung cancer increased by 66.0 for each 100 f/ml increase in asbestos exposure (relative risk rate: 1.66, 95 confidence interval: 1.53 to 1.79).
Radon is a colorless, odorless and tasteless inert gas which is radioactive. When inhaled by human, the radioactive particles produced by radon decay can cause radiation damage to human respiratory system and cause lung cancer. The radon content around uranium-containing mines is high, and building materials are the most important source of indoor radon. Such as granite, brick sand, cement and gypsum, especially natural stone containing radioactive elements. The results of three summary analyses in Europe, North America and China show that for every 100Bq/m3 increase in radon concentration, the risk of lung cancer will increase by 8 (95 confidence interval: 3 to 16), 11 (95 confidence interval: 0 to 8) and 13 (95 confidence interval: 1 to 36) respectively.
Beryllium is a basic rare metal that is used in aerospace, telecommunications, electronics, and nuclear industries. Beryllium and beryllium compounds have been classified as known human carcinogens by the U.S. National Toxicology Office.
Nickel is a naturally occurring metallic element found in the earth’s crust. Nickel metal and its compounds are widely used in industrial processes, such as nickel refining and electroplating. Nickel was recognized as a Group I carcinogen by the International Agency for Research on Cancer in 1987. In vitro studies in China have confirmed that nickel compounds (e.g., nickel chloride) activate the TLR4 signaling pathway in human lung cancer cells and that TLR4/MyD88 signaling promotes nickel-induced invasiveness of human lung cancer cells.
Indoor soot exposure is a risk factor for lung cancer, and a Meta-analysis of a Chinese population study by Zhao et al. showed that indoor soot exposure increased the risk of lung cancer by 1.42-fold (ratio: 2.42, 95 confidence interval: 1.62-3.63) and increased the risk of lung cancer in women by 1.52-fold (ratio: 2.52, 95 confidence interval: 1.94-3.28).
4. Family history and genetic susceptibility to lung cancer
Family aggregation is present in patients with lung cancer. These findings suggest that genetic factors may play an important role in the population and/or individuals who are susceptible to environmental carcinogens. Among non-smokers, the adjusted ratio was 1.51 (95 confidence interval: 1.11-2.06). The genetic susceptibility of lung cancer is now considered to be based on genetic polymorphisms involved in the metabolism of carcinogens, genomic instability, DNA repair, and regulation of cell proliferation and apoptosis, of which metabolic enzyme genes and DNA damage repair genes are the two most studied aspects.
5. Other factors
Other factors associated with the development of lung cancer include nutrition and diet, physical activity, immune status, estrogen levels, infections (human immunodeficiency virus, human papilloma virus), chronic inflammation of the lung, and economic and cultural levels, but their association with lung cancer is controversial and needs further study and evaluation.