The diagnosis of lung cancer typically begins with the detection of a mass or a suspicious appearance on a chest X-ray. The patient's medical history, tobacco use (cigarettes, pipes, cigars, etc.), environmental or occupational exposures, and family history of cancer are thoroughly evaluated. In cases of suspected lung cancer, a doctor may request sputum cytology (microscopic examination of material obtained from the bronchial mucosa through a deep cough). This test is a simple and useful screening method for detecting cancer cells. For a definitive diagnosis, examination of lung tissue (biopsy) is necessary. This is critically important for determining the type of cancer (small cell or non-small cell) and its spread (metastasis) or stage. The approach to accessing the mass is usually determined under computed tomography (CT) guidance, utilizing methods such as fine-needle biopsy or bronchoscopy. The diagnosis of lung cancer is confirmed following the pathological examination of the biopsy material. If the disease has spread to other organs, biopsies from these organs may also be taken to support the diagnosis. Once diagnosed, the disease is staged. Lung cancer is a type of cancer not included in current cancer screening programs, making early detection (before spread to lymph nodes or other organs) rare. The probability of catching the disease in an early stage is approximately 15%. While the 5-year survival rate for cases that have not spread to lymph nodes is 50%, this rate typically falls below 15% because the disease has often spread to nearby organs outside the lung by the time of diagnosis. Early diagnosis usually occurs incidentally during routine check-ups or examinations performed for another health issue.