Lung cancer occurs in the bronchial mucosa epithelium, also known as bronchial cancer. In the past 50 years, many countries have reported a significant increase in the incidence of lung cancer, which has taken the first place among male cancer patients and is also rapidly increasing in women, accounting for the second or third most common malignant tumor among women. The cause of lung cancer is still not completely clear, but a lot of information shows that long-term heavy smoking is an important causative factor of lung cancer. The incidence of squamous and undifferentiated lung cancer is 4 to 10 times higher than that of nonsmokers who smoke more than 40 cigarettes per day for many years. The incidence of lung cancer in urban residents is higher than that in rural areas, which is related to atmospheric pollution and the presence of carcinogenic substances in cigarette smoke.
Causes of lung cancer
1.Smoking
Tobacco contains more than 3000 kinds of chemicals, among which multi-chain aromatic hydrocarbon compounds (such as benzo(a)pyrene) and nitrosamines have strong carcinogenic activity. Multi-chain aromatic hydrocarbons and nitrosamines can cause DNA damage to bronchial epithelial cells through various mechanisms, resulting in activation of oncogenes (e.g. Ras gene) and inactivation of oncogenes (e.g. p53, FHIT gene, etc.), which can lead to cell transformation and eventually carcinogenesis.
2.Occupational and environmental exposure
Lung cancer is one of the most important occupational cancers. The following nine occupational environmental carcinogens have been proven to increase the incidence of lung cancer: by-products of aluminum products, arsenic, asbestos, bis-chloromethylether, chromium compounds, coke ovens, mustard gas, impurities containing nickel, and vinyl chloride. Long-term exposure to beryllium, cadmium, silicon, formalin and other substances can also increase the incidence of lung cancer. Air pollution, especially industrial waste gas, can trigger lung cancer.
3.Ionizing radiation
The lung is a more sensitive organ to radiation. Ionizing radiation can induce lung tumor.
4.Past chronic lung infections
For example, in patients with tuberculosis and bronchiectasis, the bronchial epithelium may become squamous epithelium in the process of chronic infection, resulting in cancer.
5.Heredity and other factors
Family gathering, genetic susceptibility, lowered immune function, metabolic and endocrine dysfunction may also play an important role in the occurrence of lung cancer.
6.Atmospheric pollution
The high incidence of lung cancer in developed countries is mainly due to the pollution of the atmosphere with harmful substances such as benzo(a)pyrene carcinogenic hydrocarbons produced by burning oil, coal and internal combustion engines and asphalt road dust in industrial and transportation developed areas. Atmospheric pollution and smoking may have a synergistic effect on the incidence of lung cancer.
Clinical manifestations of lung cancer
The clinical manifestations of lung cancer are complex. The presence or absence of symptoms and signs, their severity and their early or late appearance depend on the location of tumor, pathological type, the presence or absence of metastasis and complications, as well as the differences in patients’ response and tolerance. Early symptoms of lung cancer are often mild and may even be uncomfortable. The symptoms of central lung cancer appear early and heavy, while the symptoms of peripheral lung cancer appear late and light, or even asymptomatic, and are often detected during physical examination. The symptoms of lung cancer are broadly divided into: local symptoms, systemic symptoms, extra-pulmonary symptoms, infiltration and metastasis symptoms.
(I) Local symptoms
Local symptoms refer to the symptoms caused by irritation, obstruction, infiltration and compression of tissues when the tumor itself grows locally.
1.Cough
Cough is the most common symptom. 35% to 75% of patients have cough as the first symptom. Cough caused by lung cancer may be related to changes in bronchial mucus secretion, obstructive pneumonia, pleural invasion, pulmonary atelectasis and other intrathoracic comorbidities.
2.Blood in sputum or hemoptysis
Blood in sputum or hemoptysis is also a common symptom of lung cancer, and this is the first symptom in about 30% of cases. Due to the rich blood supply and brittle texture of the tumor tissue, the blood vessels may rupture and cause bleeding during severe coughing, and coughing blood may also be caused by local necrosis or vasculitis of the tumor.
3.Chest pain
Chest pain is the first symptom of about 25% of patients. It often appears as irregular hidden pain or dull pain in the chest. In most cases, peripheral type lung cancer invades the wall pleura or chest wall, which can cause sharp and intermittent pleural pain, and if it continues to develop, it will evolve into a constant drilling pain.
4. Chest tightness and shortness of breath
About 10% of patients have this as the first symptom, mostly seen in central type lung cancer, especially in patients with poor lung function. The causes of dyspnea mainly include.
① When lung cancer is advanced and mediastinal lymph nodes metastasize extensively and compress the trachea, rhomboid or main bronchus, shortness of breath or even asphyxia may appear.
② When a large amount of pleural effusion compresses the lung tissue and causes serious displacement of the mediastinum, or when there is pericardial effusion, chest tightness, shortness of breath and dyspnea may also appear, but the symptoms can be relieved after fluid extraction.
③Diffuse fine bronchoalveolar carcinoma and bronchial disseminated adenocarcinoma, which reduce the breathing area and impair gas diffusion function, leading to severe ventilation/blood flow ratio imbalance, causing progressive worsening of dyspnea, often accompanied by cyanosis.
④Other: including obstructive pneumonia. Pulmonary atelectasis, lymphangiostasis, tumor microembolism, upper airway obstruction, spontaneous pneumothorax, and combined chronic lung diseases such as COPD.
5, hoarseness
Hoarseness is the first complaint of 5% to 18% of lung cancer patients, usually accompanied by cough. Hoarseness generally indicates direct mediastinal invasion or lymph node growth involving the ipsilateral recurrent laryngeal nerve and resulting in left vocal fold paralysis.
(B) Systemic symptoms
1. Fever
Fever is the first symptom of lung cancer in 20%-30% of cases. One is inflammatory fever. Antibiotic treatment may be effective and the shadow may be absorbed, but it often recurs due to poor drainage of secretions. The second is cancer fever, which is mostly caused by the absorption of tumor necrotic tissues by the body.
2.Wasting and cachexia
Late stage of lung cancer can cause severe wasting, anemia and cachexia due to the loss of appetite caused by infection and pain, increased consumption caused by tumor growth and toxins, and increased levels of cytokines such as TNF and Leptin in the body.
Dissemination and metastasis of lung cancer
1.Direct diffusion
Tumors near the periphery of the lung may invade the dirty pleura, and cancer cells are shed into the pleural cavity to form implantation metastasis. Tumors of central type or near the mediastinal surface may invade the pleura of dirty wall layer, chest wall tissue and mediastinal organs.
2.Bloodstream metastasis
After the cancer cells return to the left heart with the pulmonary vein, they can be metastasized to any part of the body. The common metastatic sites are liver, brain, lung, skeletal system, adrenal gland, pancreas and other organs.
3.Lymphatic tract metastasis
Lymphatic tract metastasis is the most common metastasis route of lung cancer. Cancer cells first invade the lymph nodes around the adjacent lung segments or lobes through the lymphatic vessels around the bronchi and pulmonary vessels, then reach the lymph nodes under the hilum or bullae, then invade the mediastinal and paratracheal lymph nodes, and finally involve the supraclavicular or cervical lymph nodes.
Prevention of lung cancer
Lung cancer can be prevented and controlled. It can be divided into three levels of prevention: primary prevention is etiological intervention; secondary prevention is screening and early diagnosis of lung cancer to achieve early diagnosis and treatment of lung cancer; tertiary prevention is rehabilitation prevention.
Primary prevention.
1.Prohibition and control of smoking
Foreign studies have proved that quitting smoking can significantly reduce the incidence of lung cancer, and the sooner you quit smoking, the more obvious the reduction of lung cancer incidence. Therefore, quitting smoking is the most effective way to prevent lung cancer.
2.Protect the environment
It has been proved that the exposure dose of air pollution, deposition index, smoke index, benzo(a)pyrene, etc. is positively correlated with the incidence of lung cancer, so protecting the environment and reducing air pollution are important measures to reduce the incidence of lung cancer.
3.Prevention of occupational factors
It has been recognized that many occupational carcinogens increase the incidence of lung cancer, and reducing the exposure to occupational carcinogens can reduce the incidence of lung cancer.
4.Scientific diet
Increasing vegetables and fruits in the diet can prevent lung cancer.