Comment se diagnostique le cancer du poumon ?

The discovery of lung cancer occurs in three different ways. Most often, cancer is diagnosed when symptoms, either local or general, or related to metastases, arise.

It can also be diagnosed incidentally, for example, during a chest X-ray or CT scan performed for another reason such as preoperative assessment or after an accident.

Finally, lung cancer may be diagnosed as a result of a screening program.

Imaging exams

To establish a diagnosis of lung cancer, several examinations will be necessary.

The first of these will be a clinical examination by a physician, whether it be your referring physician, a pulmonologist, or an oncologist. They will particularly examine the chest and check the lymph nodes located in the neck.

If not already done, various imaging tests will be prescribed. These aim to establish or confirm a diagnosis of lung cancer and assess the extent of the cancer. A chest X-ray provides a two-dimensional image, allowing the assessment of lung condition and the presence of any anomalies.

A computer tomography (CT) scan of the chest and upper abdomen provides more precise, three-dimensional images.

It helps to locate a tumor and determine if lymph nodes are invaded by cancer cells. This painless examination takes about 10 to 30 minutes.

A brain CT scan or Magnetic Resonance Imaging (MRI) will exclude or confirm whether the cancer has spread to the brain. MRI provides particularly detailed images. Injection of a contrast agent into a vein in the arm may be necessary for clearer images.

This painless examination may be slightly uncomfortable as the patient must lie on an examination table that slides inside a ring for about 30 minutes.

Finally, a Positron Emission Tomography (PET) scan combined with a CT scan provides information on tissue activity, particularly its ability to absorb a radioactive molecule similar to glucose.

Cancer cells absorb this molecule more strongly than normal cells, enabling the localization of the primary tumor and any metastases throughout the body.

By superimposing the images given by the PET scan and those given by the CT scan, the radiologist can better locate cancerous tissues. The examination is performed about an hour after the injection of the slightly radioactive substance to allow for its distribution.

These various imaging examinations help to assess the extent of the disease.

However, only a histological examination performed under a microscope by a pathologist will establish the exact diagnosis of the disease and the nature of the cancer.

Histological diagnosis

This examination is done from either a biopsy or a surgical specimen.

There are several techniques to obtain a biopsy :

• bronchoscopy allows examination of the inside of the respiratory tract and collection of tissue samples using a flexible tube called a bronchoscope. This tube is inserted through the natural openings (nose or mouth). The examination is performed under local anesthesia.
• A biopsy can also be obtained using a needle guided by CT or ultrasound. The histological examination can also be performed on cells obtained by bronchoscopy after bronchoalveolar lavage. This lavage involves injecting a slightly saline solution into the lungs to collect any cancer cells that may be present.

By examining under a microscope, the cells present in the biopsy, in an operation specimen or in the alveolar lavage (histological examination), the pathologist can determine the exact nature of the lung cancer.

He will also be able to study certain characteristics of the cancer cells, such as the expression of PD-L1, an immune system checkpoint.

Molecular analysis

If the previous examinations reveal the presence of lung cancer, it will often be necessary to analyze the DNA of cancer cells. This so-called "molecular" analysis is performed in specialized laboratories in molecular biology using tissue samples and DNA sequencing techniques.

There are new techniques that allow for the rapid analysis of a large number of genes.

Some of these genes may have modifications that lead to the production of abnormal proteins, possibly responsible for uncontrolled multiplication of cancer cells. These abnormal proteins can then be targeted by drugs that block their function.

To treat lung cancer, these targeted therapies can only be chosen by the physician after obtaining the results of the molecular analysis, hence the need for it to be performed as quickly as possible.

Ultimately, all the examinations performed (clinical examination, medical imaging, histological examination, molecular analysis) will establish the precise nature of lung cancer and its possible spread to lymph nodes or to another organ.