What is lung cancer ?
Primary lung cancers, also known as bronchial cancers, originate in the cells of the lungs.
In France, lung cancer is the second most common cancer in men, behind prostate cancer. In women, it is the third most common cancer, after breast cancer and colorectal cancer (Source: National Cancer Institute).
Since 1990, the number of cases has remained stable in men but has significantly increased in women (+5.2% per year on average). The majority of lung cancer cases are diagnosed in patients aged 65 and over.
It is the leading cause of cancer death in men.
TO REMIND YOU
The lungs , located in the chest on each side of the heart, are part of the respiratory system.
These vital organs enable breathing, allowing our bodies to be supplied with oxygen and to eliminate carbon dioxide (CO2). The right lung consists of three parts called lobes , and it is larger than the left lung, which has two lobes. These lobes further subdivide into lobules . The bronchi , which carry air from the trachea to the lungs, divide inside the lungs into primary, secondary, and tertiary bronchi, and then into bronchioles .
The trachea, bronchi, and bronchioles have mucous glands that produce mucus, which helps to eliminate air impurities. Each bronchiole branches within its lobule. The final branches, called terminal bronchioles, open into small spherical cavities called pulmonary alveoli , which are richly vascularized. The lungs contain approximately 200 million pulmonary alveoli, providing an exchange surface between air and our blood vessels of about 100 m2, which is 50 times the surface area of the skin.
The lungs are surrounded by a very thin membrane, the pleura, consisting of two layers separated by a space, the pleural cavity. One layer is in direct contact with the lungs, while the other lines the inside of the thoracic cavity. Between the two lungs lies a space, the mediastinum .
Like other cancers, lung cancers result from uncontrolled cell proliferation. There are different types of lung cells, leading to various types of lung cancers depending on the cells that initiate the cancer.
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The exact nature of a cancer is determined by a pathologist, a medical specialist in anatomical pathology , a medical specialty that involves examining organs, tissues, or cells to contribute to the diagnosis of a disease or establish that diagnosis.
For this, the pathologist will need a small piece of tissue ( biopsy ) or a surgical specimen. This will be studied and then sliced into thin sections that will be treated with different stains and reagents.
After staining and treatment, these thin sections will be examined under a microscope ( histological examination ) to determine the exact nature of the cancer cells. It will take about a week to obtain the result of the histological examination.
Lung cancers are divided into Non-Small Cell Lung Cancers (NSCLC) and Small Cell Lung Cancers (SCLC). It is important to distinguish between these two types of cancers because their management and treatments differ.
Small cell cancers are often aggressive and proliferate very rapidly. It is therefore a therapeutic emergency that needs to be addressed without delay. Non-small cell cancers progress more slowly.
Non-small cell lung cancers
The most common lung cancers are non-small cell lung cancers, which represent 85% of lung cancers.
Among these non-small cell cancers, are distinguished squamous cell carcinomas, adenocarcinomas, large cell carcinomas and undifferentiated carcinomas.
- Squamous cell carcinomas represent approximately 25-30% of all lung cancers. These cancers originate in the large bronchi from thin, flat cells called squamous cells. They are more common in men and are generally caused by smoking.
- Adenocarcinomas represent approximately 40% of all lung cancers. They develop in the peripheral areas of the lung, particularly in the upper lobes and near the pleura. Tumor proliferation occurs from cells that produce mucus. This is the most common type of lung cancer in women and in non-smokers.
- Large cell carcinomas and undifferentiated carcinomas are rarer and represent approximately 10 to 15% of all lung cancers. Large cell carcinomas can develop and spread very rapidly.
Small cell lung cancers
Small cell cancers represent 15% of lung cancers. They are often large tumors developed from the large bronchi in the center of the lungs. These cancers are the most aggressive of lung cancers. They mainly affect individuals over 70 years old, heavy smokers, or former heavy smokers.
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Lung adenocarcinomas present multiple alterations in their DNA . These alterations lead to the expression of abnormal proteins by cancer cells.
These proteins are often receptors for growth factors that are on the surface of cancer cells or intracellular proteins that transmit signals within cells.
The abnormal proteins lead to continuous activation of tumor cells and their multiplication. They explain the occurrence of cancer, especially in non-smokers. Blocking these proteins, which can cause the death of tumor cells, makes them particularly interesting targets for so-called "targeted" therapies.
The cancerous lung cells have the potential to leave the lung and invade other organs. They can then form new tumors, which are extensions of the primary cancer.
These new tumors are called metastases and are composed of cancerous lung cells. Metastases particularly form in the liver, bones, brain, or adrenal glands.
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While lung cancers can form metastases away from the lung , other cancers such as breast cancer, colorectal cancer, kidney cancer, head and neck cancer, testicular cancer, bone cancer, thyroid cancer, or melanoma can form metastases in the lung.
These lung metastases are not composed of lung cells but of cancer cells originating from another organ.
Interview with Professor Marie Wislez
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Article updated on 27 sept. 2024
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