The main cause and risk factors of lung cancer: 1 smog has been recognized as the most important carcinogen of lung cancer. Occupational factors causing lung cancer: At present, occupational exposure to the following substances is considered to be related to the occurrence of lung cancer: asbestos, arsenic compounds, chromium compounds, nickel compounds, dichloromethyl ether, ionizing radiation, mustard gas, polycyclic aromatic hydrocarbons in smoke and dust, tar and oil. 3 Environmental pollution such as air pollution: If industrial waste gas is not handled properly, it can pollute the environment and atmosphere inside and outside factories and mines. In addition, a lot of coal, diesel, gasoline, asphalt pavement and motor vehicles burned every day in cities will lead to air pollution in densely populated areas. The stone, paint, floor glue, plastic ornaments and adhesives used in indoor decoration have brought indoor pollution. 5 kitchen cooking fumes and indoor fires pollute indoor air 6 indoor radon pollution: radon is a radioactive substance, which widely exists in natural soil, rocks and building materials. Other risk factors of lung cancer: previous lung diseases, such as tuberculosis, pneumonia, chronic bronchitis and emphysema. Under the influence of internal and external factors, multi-gene mutation of oncogene and tumor suppressor gene in human body causes multi-stage damage and repair errors of cells, which eventually leads to cancer. It is known that oncogene ras, myc, Rb and tumor suppressor gene p53 are related to the occurrence of lung cancer. The typical symptoms of lung cancer are cough, blood in sputum, chest pain, shortness of breath and other lung manifestations; However, according to statistics, about half of patients with lung cancer are initially extrapulmonary symptoms, which often appear before pulmonary symptoms and become an early signal of lung cancer. However, because these symptoms do not seem to indicate lung cancer, people often misdiagnose it as other diseases, so we should be alert and pay attention to mastering these signals, which will help early diagnosis and early treatment. What are the main extrapulmonary symptoms of lung cancer? 1. Bone and joint symptoms: This kind of symptom is more common. Because lung cancer cells can produce some special endocrine hormones (heterologous sex hormones), antigens and enzymes, these substances act on bone joints, causing swelling and pain of bone joints, often involving tibia, fibula, ulna, radius and other bone joints, and the ends of fingers and toes often swell into clubbed fingers. X-ray examination showed periosteal hyperplasia. 2, shoulder and back pain: Peripheral lung cancer often develops backward and upward, eroding pleura, involving ribs and chest wall tissue, thus causing shoulder and back pain. Such patients rarely have respiratory symptoms. 3, hoarseness: lung cancer metastasis oppresses the laryngeal nerve, which can paralyze the vocal cord veneer and cause hoarseness. Metastasis of lung cancer can occur in the early stage, and sometimes it can grow faster than the primary focus, so the clinical manifestations of metastasis can appear before the primary focus. 4. Nervous system symptoms: brain metastasis of lung cancer can cause nervous system symptoms such as headache, vomiting, sudden coma, aphasia and hemiplegia. Because the pulmonary symptoms are not obvious, they are often misdiagnosed as thrombosis and brain tumors. 5. Male breast hypertrophy: About 10%-20% of male lung cancer patients have breast hypertrophy, unilateral hypertrophy, but mostly bilateral hypertrophy, and this symptom appears about one year earlier than lung symptoms such as cough, blood in sputum, chest pain and shortness of breath. This is because some lung cancer cells can secrete chorionic gonadotropin, which causes hyperplasia of breast tissue and hypertrophy of breast. The thoracic cavity is a very complicated space. Three quarters of the lung surface is surrounded by the chest wall, which consists of a thin layer of intima (parietal pleura), fat, muscle, ribs and skin in different proportions. Tumors invading any of the above parts will cause pain. Therefore, most lung cancer patients with regional spread in the chest have symptoms of chest pain. A special area of the chest wall is formed at the top of the lung, that is, around the apex of the lung. The cervical nerve fibers that dominate the sensation and movement of the upper limb enter the upper limb through this area. Therefore, if the tumor invades this area, you will often feel the pain and fatigue of the affected upper limb. As a kind of lung cancer, this so-called "Pan-Koster cancer", or superior sulcus cancer, often takes shoulder pain as the main symptom. This kind of pain often needs analgesics to relieve it. Usually, such patients are easily sent to plastic surgeons or neurologists for treatment, thus losing the opportunity of early diagnosis. Nearly a quarter of the lung surface is adjacent to the so-called "mediastinum", which means "the middle part of the chest" and represents a space containing a series of living organs. The mediastinum is located directly behind the sternum and is considered as the "central area" in non-professional fields. The trachea and main bronchus pass through the mediastinum. The esophagus clings to the back of the trachea and extends downward through the trachea. The heart and its great vessels, as well as some great nerves related to life, also pass through this area. If cancer invades the mediastinum, the following symptoms may appear: ● hoarseness is the most common symptom. The recurrent laryngeal nerve, which controls the left pronunciation function, goes down from the neck to the chest, bypasses the great vessels of the heart and goes up to the throat, thus dominating the left side of the pronunciation organ. Therefore, if the tumor invades the left mediastinum and compresses the recurrent laryngeal nerve, there will be hoarseness, but there will be no symptoms of upper respiratory tract infection such as sore throat; ● There is superior vena cava on the right side of mediastinum, which transfuses venous blood of upper limbs and head and neck to the heart. If the tumor invades the right mediastinum and compresses the superior vena cava, it will initially make the jugular vein swell due to poor reflux, and finally lead to edema of the face and neck, which needs timely diagnosis and treatment. 4. Invasion of pleura can cause pleural effusion, which is often bloody. A large amount of fluid accumulation can lead to shortness of breath. In addition, cancer invades the pleura and chest wall, which can cause persistent and severe chest pain. 5. The lung at the top of the upper lobe can invade and oppress the organs and tissues located at the upper thoracic orifice. Such as the first rib, subclavian artery and vein, brachial plexus nerve, cervical sympathetic nerve, etc. , severe chest pain, upper limb vein swelling, edema, arm pain and upper limb dyskinesia, ipsilateral upper eye and facial ptosis, pupil contraction, enophthalmos, facial anhidrosis and other cervical sympathetic nerve syndrome groups. After hematogenous metastasis of lung cancer, different symptoms are produced according to the invasion of organs. Finally, almost all patients with lung cancer with regional spread have different degrees of shortness of breath. Normal tissue fluid produced by lung and myocardium is refluxed from lymph nodes in the middle of chest. If these lymph nodes are blocked by tumors, these tissue fluids will accumulate in the pericardium to form pericardial effusion or accumulate in the chest cavity to form pleural effusion. Both of the above conditions will lead to shortness of breath. However, because many smokers have different degrees of chronic lung diseases, it is difficult to distinguish shortness of breath. In addition, because some lung tissues lose their respiratory function due to tumors, their respiratory function is impaired, which leads to respiratory discomfort. At first, this discomfort only appeared during exercise, and finally it was felt even during rest.