The lung is an important organ in the respiratory system. It is located near the spine in the chest and is composed of the right lung and the left lung.
Between exhaling and inhaling, the lungs will deliver oxygen to the blood through the alveolar wall. At the same time, carbon dioxide leaves the blood and enters the alveoli, and is discharged through the lungs.
Lung can not only help us breathe, but also adjust the pH value of blood, filter out small thrombi formed in veins, adjust the concentration of biological substances and drugs in blood, participate in water metabolism, produce a variety of hormones, etc.
At the same time, lung is also one of the main places for human body to produce platelets, which can synthesize 10 million platelets per hour, accounting for about 50% of the total output of platelets.
However, such a powerful and important organ is prone to cancer. The American Cancer Society’s estimates for lung cancer in the United States for 2022 are:
- About 236,740 new cases of lung cancer (117,910 in men and 118,830 in women)
- About 130,180 deaths from lung cancer (68,820 in men and 61,360 in women)
Why Do Cancer Cells Appear?
The human body contains billions of cells, which will undergo apoptosis. In order to maintain the growth and repair of the body, cells will divide.
Generally speaking, the mother cell will divide into two daughter cells, which can be used to build new body tissue or replace cells that die due to aging and damage. When the human body no longer needs more daughter cells, cell division will end.
However, in the process of cell division, some cells have a genetic mutation that causes their genetic factors to become abnormal, causing the cells to develop "superpowers" that the human body cannot afford. These cells will not apoptosis like normal cells, and can replicate themselves without limitation. This kind of cells is cancer cells.
What are the consequences of the wanton growth of cancer cells?
Most directly, if cancer cells are in the primary focus, they will occupy the space of the focus and constrict the tissue or nerve.
In addition, cancer cells do not have the function of normal cells:
- They will not resist the invasion of bacteria or viruses like white blood cells and T cells;
- They will not transport nutrients and carbon dioxide like red blood cells;
- They don't repair body damage like platelets.
However, they will rob the nutrition of normal cells. Compared with normal cells, cancer cells need more nutrients to grow. In order to divide continuously, cancer cells absorb nutrients very quickly.
Cancer cells can also invade the boundary of normal cells and transfer to all parts of the body through blood vessels or lymphatic vessels by taking advantage of their own infiltration and metastasis. If cancer cells are allowed to develop, the nutritional supply of normal cells in the body will be insufficient, resulting in the failure of various functions to maintain the operation of the human body.
3 Key Conditions Leading to Lung Cancer
If the inner wall cells of the main bronchi and lungs have gene mutations and meet the following three conditions, lung cancer may occur:
Not all gene mutations can lead to cancer, but several key gene mutations contain pathogenic factors. Over time, the mutated cancer cells keep dividing, and then form cancer.
For example, EGFR gene mutation is one of the most common mutations in non-small cell lung cancer. It is estimated that EGFR mutations account for 40% - 50% in adenocarcinoma (a kind of lung cancer).
2. Cancer Cells Escaped from the Supervision of the Immune System
The immune system has the ability to defend against diseases. When pathogenic factors are found, the immune system will mobilize various cells in the body to prevent the occurrence or deterioration of diseases.
However, in order to avoid the attack of the immune system, cancer cells can disguise as normal cells to escape the supervision of the immune system, and then continue to divide and eventually form cancer.
3. Cumulative Time
Unlike lung cancer in children, primary lung cancer in adults does not occur suddenly.
It is a long process from the generation of the first cancer cell to the discovery of cancer, which takes about 10 to 20 years. At the beginning, the tumor grows slowly, and once it becomes malignant, it will accelerate its growth.
One cancer cell can divide and multiply into two, two can multiply into four, four can multiply into eight, eight can multiply into sixteen.
This process is called exponential growth, with the doubling time getting shorter and shorter, and the tumor growing faster.
6 High Risk Factors for Lung Cancer
High risk factors for lung cancer can be classified into the following six points:
1. Smoking and Passive Smoking
- Long-term heavy smoking is the most important carcinogenic factor of lung cancer. The greater the amount of smoking and the longer the smoking time, the higher the risk of lung cancer.
- Passive smoking is also a risk factor for lung cancer, which is more common in women.
2. Radiological Factors
- Natural stones containing radon and other radioactive elements, such as granite, brick sand, cement and gypsum. Radioactive particles with radon decay can cause radiation damage in human respiratory system and cause lung cancer.
- Large doses of ionizing radiation are also the pathogenic factors of lung cancer.
3. Occupational Exposure History
- Asbestos, chromium, nickel, copper, tin, arsenic, radioactive substances and other carcinogens exist in the working environment of industrial production and mining areas. Long term exposure to the above carcinogens can increase the risk of lung cancer.
4. Air Pollution
- Outdoor pollution: Industrial exhaust, automobile exhaust, haze, etc. contain Group I carcinogens recognized by the World Health Organization.
- Indoor microenvironment pollution: Includes soot from indoor coal combustion, lampblack from kitchen cooking, carcinogens released by indoor decoration materials, etc.
5. Heredity and Gene
- Family aggregation: There is family aggregation in lung cancer patients. If there are lung cancer patients in the family, the risk of lung cancer in their relatives will increase.
- Gene mutation: Abnormal structure and function like EGFR mutant gene, ALK fusion gene, etc. are closely related to the occurrence of lung cancer.
6. Lung Disease
- The American Cancer Society lists tuberculosis as one of the causes of lung cancer. The risk of lung cancer in tuberculosis patients is 10 times that of normal people.
- Some chronic lung diseases (such as chronic obstructive pulmonary disease, pulmonary nodules, idiopathic pulmonary fibrosis, scleroderma), viral infection, mycotoxins (aspergillus flavus), etc., may also be related to the occurrence of lung cancer.
Although lung cancer is the "first killer" of cancer deaths, it is a preventable cancer. For the above groups with high-risk factors, it is recommended to start lung cancer screening at the age of 50, with the methods like Low Dose Spiral CT (LDCT) .
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2. Lefrançais, E., Ortiz-Muñoz, G., Caudrillier, A. et al. The lung is a site of platelet biogenesis and a reservoir for haematopoietic progenitors. Nature 544, 105–109 (2017).