How “close” are you to lung cancer if you smoke? Lungs are the main component of human respiratory system, which is an important organ for inhaling oxygen, expelling carbon dioxide and maintaining normal metabolism of human body. The lungs are located on both sides of the heart in the chest cavity and are divided into the left lung and the right lung. The left lung is divided into two lobes, and the right lung is divided into three lobes, the upper, middle and lower. Each lung lobe is connected to the trachea by a tube called a bronchus. As they branch out, the bronchi become progressively thinner, and are called bronchioles, fine bronchioles, terminal fine bronchioles, respiratory fine bronchioles, alveolar tubes, etc. The most terminal branches of the bronchioles are sac-like and are called alveoli. There are nearly 300 million alveoli in our lungs. The alveolar ducts and alveoli are surrounded by capillaries, which is the place where the body and the outside world exchange oxygen and carbon dioxide. Oxygen passes through the alveolar walls, is absorbed by the blood and transported to all parts of the body, and carbon dioxide and other waste gases produced by the body are transported by the blood to the lungs, enter the alveoli through the alveolar walls, and are eventually expelled with breathing. The total area of adult alveoli is 80-100 square meters, and some alveoli are normally closed, while all alveoli are involved in gas exchange during strenuous activities. The lungs of normal people are moist red, while smokers in general have different colored lungs due to the large amount of residual smoke toxicity in their bodies, or what we call “colorful lungs”. The color of the lungs gradually deepens as the time spent smoking increases, and the color of the lungs does not return even when smoking is stopped. Here are some pictures of smokers’ lungs to warn you. Lung cancer is a cancer that originates in the bronchial epithelium or alveolar epithelium, medically known as primary bronchopulmonary cancer. Lung cancer is the most common malignant tumor in lung. Bronchial epithelial cells or alveolar epithelial cells in lung tissue malignantly change into cancer cells under the action of various carcinogenic factors, and the cancer cells grow and multiply without control, and gradually expand in size to form solid tumors. Most of the lung cancers occur in bronchi and grow to the periphery and the center of the lung; a few of them occur in alveoli and spread to other parts along the bronchial wall. Besides growing in the lung, cancer cells can also enter the lymphatic vessels and metastasize to lymph nodes; enter capillaries and metastasize with blood circulation to various parts of the body, such as liver, bones, skull and other organs. Lung cancer is now the fastest growing malignant tumor in China, and the incidence rate of lung cancer among Beijingers was 71/100,000 in 2004, while it was 49/100,000 eight years ago. In other words, the incidence rate of lung cancer among Beijingers has nearly doubled in 8 years. The mortality rate of lung cancer is also leading among malignant tumors, with one out of every four male malignant tumor patients being a lung cancer patient and one out of every five female malignant tumor patients being a lung cancer patient. The yearly increase in the number of smokers in China is considered the main reason for the high incidence and high mortality rate of lung cancer. Statistics show that the smoking rate of adult males in Beijing is 58.6% and 5.7% for females. If the current smoking situation in China remains unchanged, nearly 100 million men within the age of 29 now will die from smoking in middle or old age by 2050. The number of female deaths would also reach millions. Youth smoking is on the rise, and as long as tobacco production and sales are legal, people will smoke, and non-toxic cigarettes will exist. Smoking has been recognized as the number one cause of lung cancer. And it has been shown to have an additive relationship with age of smoking initiation, number of years of smoking, number of cigarettes smoked per day, and type of cigarette. Long-term heavy smokers are 10 to 20 times more likely to develop lung cancer than non-smokers. The younger the age of smoking initiation, the higher the incidence of lung cancer. A person who smokes 15 to 20 cigarettes a day is 14 times more likely to develop lung cancer than a nonsmoker. In China, smoking is the main risk factor for lung cancer in men, and the increase in cigarette consumption is an important reason for the rising trend of lung cancer in men. The rapid rise in the incidence of lung cancer in our country now may be reflecting the rapid rise in cigarette consumption in China after the 1970s. According to statistics, our per capita cigarette consumption is already the highest in the world, and we are one of only six countries in the world where per capita cigarette consumption still continues to rise. If this trend continues unchanged, the rising trend of lung cancer will continue until after 2020. By that time, the country is likely to have the highest incidence of lung cancer in the world. In China, lung cancer in women is not as closely related to smoking as in men, with smoking explaining only 24-35% of the causes of lung cancer. The occurrence of squamous lung cancer in women has been shown to be very closely related to smoking, but lung adenocarcinoma in women is weakly related to smoking. In recent years, as the proportion of lung cancer and adenocarcinoma in women has increased, it may suggest new changes in the characteristics of environmental risk factors.