In medicine, lung cancer staging is the assessment of the extent to which a lung cancer has spread from its original source. As with most cancers, staging is an important determinant of treatment and prognosis. In general, more advanced stages of cancer are less amenable to treatment and have a worse prognosis.

There are several methods by which this assessment is made. They are broadly classified into non-invasive techniques, which generally involve medical imaging of the lungs such as computer tomography (CT) scans, and invasive techniques such as biopsy. Invasive techniques provide additional information because tissue samples can be seen microscopically to determine the type of lung cancer and its grade.

Lung cancer is responsible for 1.3 million deaths worldwide annually, and is the most common cause of cancer-related death in men and the second most common in women. The most common cause of lung cancer is long-term exposure to tobacco smoke. Lung cancer in non-smokers, who account for approximately 15% of cases, is often attributed to a combination of genetic factors, radon gas, asbestos, and air pollution. The main types of lung cancer are non-small cell lung carcinoma and small cell lung carcinoma, the two being distinguished histologically as well as by how they are treated; non-small cell lung carcinoma is primarily treated with surgery if feasible, while small cell lung carcinoma is more frequently treated with chemotherapy and radiation.

The stage of a cancer is a description (usually numbers I to IV with IV having more progression) of the extent the cancer has spread. The stage often takes into account the size of a tumor, how deeply it has penetrated, whether it has invaded adjacent organs, how many lymph nodes it has metastasized to (if any), and whether it has spread to distant organs. Staging of cancer is the most important predictor of survival, and cancer treatment is primarily determined by staging. Thus, staging does not change with progression of the disease as it is used to assess prognosis. Patients' cancer, however, may be restaged after treatment but the staging established at diagnosis is rarely changed.

Cancer staging can be divided into a clinical stage and a pathologic stage. In the TNM (Tumor, Node, Metastasis) system, clinical stage and pathologic stage are denoted by a small "c" or "p" before the stage (e.g., cT3N1M0 or pT2N0).

Because they use different criteria, clinical stage and pathologic stage often differ. Pathologic staging is usually considered the "better" or "truer" stage because it allows direct examination of the tumor and its spread, contrasted with clinical staging which is limited by the fact that the information is obtained by making indirect observations at a tumor which is still in the body. However, clinical staging and pathologic staging should complement each other. Not every tumor is treated surgically, therefore pathologic staging is not always available. Also, sometimes surgery is preceded by other treatments such as chemotherapy and radiation therapy which shrink the tumor, so the pathologic stage may underestimate the true stage.

Lung cancer is a disease characterized by uncontrolled cell growth in tissues of the lung. If left untreated, this growth can spread beyond the lung in a process called metastasis into nearby tissue and, eventually, into other parts of the body. Most cancers that start in lung, known as primary lung cancers, are carcinomas that derive from epithelial cells. The main types of lung cancer are small cell lung carcinoma (SCLC), also called oat cell cancer, and non-small cell lung carcinoma (NSCLC). The most common cause of lung cancer is long-term exposure to tobacco smoke. Nonsmokers account for 15% of lung cancer cases, and these cases are often attributed to a combination of genetic factors,radon gas,asbestos, and air pollution including secondhand smoke.

The most common symptoms are coughing (including coughing up blood), weight loss and shortness of breath. Lung cancer may be seen on chest radiograph and computed tomography (CT scan). The diagnosis is confirmed with a biopsy. This is usually performed by bronchoscopy or CT-guided biopsy. Treatment and prognosis depend on the histological type of cancer, the stage (degree of spread), and the patient's general wellbeing, measured by performance status. Common treatments include surgery, chemotherapy, and radiotherapy. NSCLC is sometimes treated with surgery, whereas SCLC usually responds better to chemotherapy and radiation therapy. This is partly because SCLC often spreads quite early, and these treatments are generally better at getting to cancer cells that have spread to other parts of the body.