Lung cancer can remain localized in the lungs or spread (metastasize) to other parts of the body such as lymph nodes, bones, and the brain. Therefore, obtaining a tissue sample from the lung is essential for the definitive diagnosis and subtyping of lung cancer. Tissue samples obtained via biopsy are meticulously examined under a microscope. It has been scientifically proven that taking a biopsy from suspicious lesions in the lung does not cause the tumor to spread or the disease to worsen.

The main methods used to obtain these tissue samples are:

* Bronchoscopy: The airways are examined, and small tissue samples (biopsies) are taken using a thin, lighted tube inserted through the mouth or nose into the trachea and bronchi.
* Needle Biopsy (Transthoracic Needle Aspiration): A special needle is inserted through the chest wall towards the suspicious mass in the lung to obtain a sample from the tissue suspected of being cancerous. These samples are used for pathological examination.
* Thoracentesis: This procedure involves taking a sample with a needle from the fluid (pleural effusion) accumulated in the space surrounding the lungs. Cancer cells in this fluid are examined under a microscope.
* Thoracotomy (Open Biopsy): This is a surgical method applied when diagnosis cannot be made with other biopsy methods or when they are not suitable. The chest cavity is opened, and a larger sample of lung tissue is taken.
* Sputum Cytology: This method involves examining a sputum sample, which the patient coughs up deeply, under a microscope to investigate the presence of cancer cells.

After a diagnosis of lung cancer is made, additional molecular and genetic tests are performed on the samples to determine the stage and spread of the disease. As a result of these comprehensive evaluations, a personalized and most effective treatment plan is created, tailored to the stage and genetic characteristics of the cancer.