The trend of lung cancer distribution is higher in large cities than in small and medium-sized cities; Small and medium-sized cities are higher than rural areas. Industrial areas in big cities are higher than non industrial areas, and areas using coal fired stoves are higher than areas using natural gas stoves. In some areas, using coal as fuel indoors results in a higher mortality rate for lung cancer in women than in men. Due to long-term exposure to arsenic, radon and radon daughters, the incidence rate of lung cancer in some underground workers is very high.
1) Smoking factor
Smoking is widely recognized as one of the most important risk factors for lung cancer. Smokers die of lung cancer at a rate more than 10 times higher than non-smokers. In the United States, smoking accounts for 1/3 of all malignant tumor deaths, with 400,700 smoking-related deaths each year. Half of these deaths occur between the ages of 35 and 69, with an average loss of expected life of 20 to 25 years. In China, male lung cancer incidence is caused by smoking in 70% to 80% of cases, while female lung cancer is attributed to smoking and passive smoking in about 30% of cases. The earlier a person starts smoking, the greater the risk of developing lung cancer. Lung cancer mortality among those who have smoked for 60 years is about 100 times higher than among those who have smoked for 20 years. The mortality rate of lung cancer in women who are passively exposed to smoke from their husbands, who are non-smokers, is 1 to 2 times higher than in women whose husbands do not smoke. When smoking and occupational or environmental carcinogens act together to cause cancer in humans, the result is more harmful than the sum of the carcinogenic effects of each individual factor, a phenomenon known as synergy. Smoking and alcohol also have a synergistic carcinogenic effect. If a person smokes an average of 20 cigarettes per day and has smoked for 20 years, their risk of developing lung cancer is 20 times higher than that of a non-smoker. A person who starts smoking before the age of 20 has a 28-fold higher risk of dying from lung cancer than a non-smoker.
2) Occupational Lung Cancer Factors
In the 1970s, some industrial cities in China had a significantly high incidence and mortality rate of lung cancer in areas with concentrated factories. Currently, it is believed that exposure to the following substances is related to the occurrence of lung cancer: asbestos, arsenic compounds, chromium compounds, nickel compounds, dichloromethane, ionizing radiation, mustard gas, as well as polycyclic aromatic hydrocarbons in coal smoke, tar, and petroleum. Other factors suspected to be related to lung cancer include: beryllium, cadmium, lead, chlorinated vinyl, formaldehyde, etc. Asbestos workers have a sevenfold higher risk of dying from lung cancer than the general population, and the risk of lung cancer for asbestos workers who smoke is 50 to 90 times higher than the general population, due to the synergistic effect of smoking and asbestos.
3) Air Pollution and Other Environmental Pollution
Industrial exhaust gases, if not handled properly, can pollute the internal and external environments of factories and mines. In addition, the daily burning of large quantities of coal, diesel, gasoline, as well as the laying of asphalt roads and exhaust gases from vehicles in cities, can all lead to air pollution in densely populated areas. About 10% of lung cancer patients in general cities are caused by air pollution. Kitchen oil fumes and coal smoke pollution are one of the reasons for non-smoking women to develop lung cancer. In recent years, indoor decoration materials such as stone, paint, floor glue, plastic decorations, and adhesives have caused indoor pollution. According to an article in the American journal “Atmospheric Environment,” it is believed that “smog” formed by extremely fine dry dust particles such as sandstorms, dust storms, and floating dust causes a high incidence of lung cancer in China.
4) Indoor pollution
Radon is a radioactive element widely present in natural soil, rock, and building materials. The isotopes of radon and their decay products are called radon daughters. Where there is radon, there will be radon daughters, and both radon and radon daughters are harmful to human health. Radon can enter indoor spaces through foundation cracks, building joints, gaps in building material interfaces, and loose pipe entry points. It may also escape into indoor spaces from building materials. China’s indoor air radon concentration standard is 100 Becquerels per cubic meter. Since 1994, China has investigated 1,524 office buildings and homes in 14 cities, finding that 6.8% had excessive radon levels. Internationally, it is believed that people exposed to a radon concentration of 300-500 Becquerels per cubic meter have a lung cancer mortality rate twice that of those exposed to normal levels. Studies estimate that approximately 24,000 radon-induced lung cancer cases occur in the United States each year. It is considered the second leading cause of lung cancer after smoking. The World Health Organization estimates that indoor radon exposure accounts for 5%-15% of all lung cancer cases worldwide.
5) Other risk factors for lung cancer include previous pulmonary diseases such as tuberculosis, pneumonia, chronic bronchitis, and emphysema. However, compared to the four factors mentioned above, the role of previous disease history is smaller.
6) Other factors.
Under the influence of both internal and external factors, multiple gene mutations in cancer genes and tumor suppressor genes within the human body lead to multiple stages of cell damage and repair errors, eventually causing cancer. Known cancer genes such as ras, myc, Rb, and tumor suppressor gene p53 are related to the occurrence of lung cancer.